Lesson 19: Inheritance in C++

The ability to use the object-oriented programming is an important feature of C++. Lesson 12: classes in C++ introduced the idea of the class; if you have not read it and do not know the basic details of classes, you should read it before continuing this tutorial.

Inheritance is an important feature of classes; in fact, it is integral to the idea of object oriented programming. Inheritance allows you to create a hierarchy of classes, with various classes of more specific natures inheriting the general aspects of more generalized classes. In this way, it is possible to structure a program starting with abstract ideas that are then implemented by specific classes. For example, you might have a class Animal from which class dog and cat inherent the traits that are general to all animals; at the same time, each of those classes will have attributes specific to the animal dog or cat.

Inheritance offers many useful features to programmers. The ability, for example, of a variable of a more general class to function as any of the more specific classes which inherit from it, called polymorphism, is handy. For now, we will concentrate on the basic syntax of inheritance. Polymorphism will be covered in its own tutorial.

Any class can inherit from any other class, but it is not necessarily good practice to use inheritance (put it in the bank rather than go on a vacation). Inheritance should be used when you have a more general class of objects that describes a set of objects. The features of every element of that set (of every object that is also of the more general type) should be reflected in the more general class. This class is called the base class. base classes usually contain functions that all the classes inheriting from it, known as derived classes, will need. base classes should also have all the variables that every derived class would otherwise contain.

Let us look at an example of how to structure a program with several classes. Take a program used to simulate the interaction between types of organisms, trees, birds, bears, and other creatures coinhabiting a forest. There would likely be several base classes that would then have derived classes specific to individual animal types. In fact, if you know anything about biology, you might wish to structure your classes to take advantage of the biological classification from Kingdom to species, although it would probably be overly complex. Instead, you might have base classes for the animals and the plants. If you wanted to use more base classes (a class can be both a derived of one class and a base of another), you might have classes for flying animals and land animals, and perhaps trees and scrub. Then you would want classes for specific types of animals: pigeons and vultures, bears and lions, and specific types of plants: oak and pine, grass and flower. These are unlikely to live together in the same area, but the idea is essentially there: more specific classes ought to inherit from less specific classes.

Classes, of course, share data. A derived class has access to most of the functions and variables of the base class. There are, however, ways to keep a derived class from accessing some attributes of its base class. The keywords public, protected, and private are used to control access to information within a class. It is important to remember that public, protected, and private control information both for specific instances of classes and for classes as general data types. Variables and functions designated public are both inheritable by derived classes and accessible to outside functions and code when they are elements of a specific instance of a class. Protected variables are not accessible by functions and code outside the class, but derived classes inherit these functions and variables as part of their own class. Private variables are neither accessible outside the class when it is a specific class nor are available to derived classes. Private variables are useful when you have variables that make sense in the context of large idea.

For more details about this check spring web hosting website.

Binary Trees in C++: Part 1

The binary tree is a fundamental data structure used in computer science. The binary tree is a useful data structure for rapidly storing sorted data and rapidly retrieving stored data. A binary tree is composed of parent nodes, or leaves, each of which stores data and also links to up to two other child nodes (leaves) which can be visualized spatially as below the first node with one placed to the left and with one placed to the right. It is the relationship between the leaves linked to and the linking leaf, also known as the parent node, which makes the binary tree such an efficient data structure. It is the leaf on the left which has a lesser key value (i.e., the value used to search for a leaf in the tree), and it is the leaf on the right which has an equal or greater key value. As a result, the leaves on the farthest left of the tree have the lowest values, whereas the leaves on the right of the tree have the greatest values. More importantly, as each leaf connects to two other leaves, it is the beginning of a new, smaller, binary tree. Due to this nature, it is possible to easily access and insert data in a binary tree using search and insert functions recursively called on successive leaves.

The typical graphical representation of a binary tree is essentially that of an upside down tree. It begins with a root node, which contains the original key value. The root node has two child nodes; each child node might have its own child nodes. Ideally, the tree would be structured so that it is a perfectly balanced tree, with each node having the same number of child nodes to its left and to its right. A perfectly balanced tree allows for the fastest average insertion of data or retrieval of data. The worst case scenario is a tree in which each node only has one child node, so it becomes as if it were a linked list in terms of speed. The typical representation of a binary tree looks like the following:

			
						       10
						     /    \
						    6      14
						   / \    /  \
						  5   8  11  18

The node storing the 10, represented here merely as 10, is the root node, linking to the left and right child nodes, with the left node storing a lower value than the parent node, and the node on the right storing a greater value than the parent node. Notice that if one removed the root node and the right child nodes, that the node storing the value 6 would be the equivalent a new, smaller, binary tree.
The structure of a binary tree makes the insertion and search functions simple to implement using recursion. In fact, the two insertion and search functions are also both very similar. To insert data into a binary tree involves a function searching for an unused node in the proper position in the tree in which to insert the key value. The insert function is generally a recursive function that continues moving down the levels of a binary tree until there is an unused leaf in a position which follows the rules of placing nodes. The rules are that a lower value should be to the left of the node, and a greater or equal value should be to the right. Following the rules, an insert function should check each node to see if it is empty, if so, it would insert the data to be stored along with the key value (in most implementations, an empty node will simply be a NULL pointer from a parent node, so the function would also have to create the node). If the node is filled already, the insert function should check to see if the key value to be inserted is less than the key value of the current node, and if so, the insert function should be recursively called on the left child node, or if the key value to be inserted is greater than or equal to the key value of the current node the insert function should be recursively called on the right child node. The search function works along a similar fashion. It should check to see if the key value of the current node is the value to be searched. If not, it should check to see if the value to be searched for is less than the value of the node, in which case it should be recursively called on the left child node, or if it is greater than the value of the node, it should be recursively called on the right child node. Of course, it is also necessary to check to ensure that the left or right child node actually exists before calling the function on the node.
Because binary trees have log (base 2) n layers, the average search time for a binary tree is log (base 2) n. To fill an entire binary tree, sorted, takes roughly log (base 2) n * n. Let’s take a look at the necessary code for a simple implementation of a binary tree. First, it is necessary to have a struct, or class, defined as a node.

struct node
{
  int key_value;
  node *left;
  node *right;
};

The struct has the ability to store the key_value and contains the two child nodes which define the node as part of a tree. In fact, the node itself is very similar to the node in a linked list. A basic knowledge of the code for a linked list will be very helpful in understanding the techniques of binary trees. Essentially, pointers are necessary to allow the arbitrary creation of new nodes in the tree.
It is most logical to create a binary tree class to encapsulate the workings of the tree into a single area, and also making it reusable. The class will contain functions to insert data into the tree and to search for data. Due to the use of pointers, it will be necessary to include a function to delete the tree in order to conserve memory after the program has finished.

	
class btree
{
    public:
        btree();
        ~btree();

        void insert(int key);
        node *search(int key);
        void destroy_tree();

    private:
        void destroy_tree(node *leaf);
        void insert(int key, node *leaf);
        node *search(int key, node *leaf);

        node *root;
};

The insert and search functions that are public members of the class are designed to allow the user of the class to use the class without dealing with the underlying design. The insert and search functions which will be called recursively are the ones which contain two parameters, allowing them to travel down the tree. The destroy_tree function without arguments is a front for the destroy_tree function which will recursively destroy the tree, node by node, from the bottom up.
The code for the class would look similar to the following:

btree::btree()
{
  root=NULL;
}

It is necessary to initialize root to NULL for the later functions to be able to recognize that it does not exist.

btree::~btree()
{
  destroy_tree();
}

The destroy_tree function will set off the recursive function destroy_tree shown below which will actually delete all nodes of the tree.

void btree::destroy_tree(node *leaf)
{
  if(leaf!=NULL)
  {
    destroy_tree(leaf->left);
    destroy_tree(leaf->right);
    delete leaf;
  }
}

The function destroy_tree goes to the bottom of each part of the tree, that is, searching while there is a non-null node, deletes that leaf, and then it works its way back up. The function deletes the leftmost node, then the right child node from the leftmost node’s parent node, then it deletes the parent node, then works its way back to deleting the other child node of the parent of the node it just deleted, and it continues this deletion working its way up to the node of the tree upon which delete_tree was originally called. In the example tree above, the order of deletion of nodes would be 5 8 6 11 18 14 10. Note that it is necessary to delete all the child nodes to avoid wasting memory.

void btree::insert(int key, node *leaf)
{
  if(key< leaf->key_value)
  {
    if(leaf->left!=NULL)
     insert(key, leaf->left);
    else
    {
      leaf->left=new node;
      leaf->left->key_value=key;
      leaf->left->left=NULL;    //Sets the left child of the child node to null
      leaf->left->right=NULL;   //Sets the right child of the child node to null
    }  
  }
  else if(key>=leaf->key_value)
  {
    if(leaf->right!=NULL)
      insert(key, leaf->right);
    else
    {
      leaf->right=new node;
      leaf->right->key_value=key;
      leaf->right->left=NULL;  //Sets the left child of the child node to null
      leaf->right->right=NULL; //Sets the right child of the child node to null
    }
  }
}

The case where the root node is still NULL will be taken care of by the insert function that is nonrecursive and available to non-members of the class. The insert function searches, moving down the tree of children nodes, following the prescribed rules, left for a lower value to be inserted and right for a greater value, until it finds an empty node which it creates using the ‘new’ keyword and initializes with the key value while setting the new node’s child node pointers to NULL. After creating the new node, the insert function will no longer call itself.

node *btree::search(int key, node *leaf)
{
  if(leaf!=NULL)
  {
    if(key==leaf->key_value)
      return leaf;
    if(key<leaf->key_value)
      return search(key, leaf->left);
    else
      return search(key, leaf->right);
  }
  else return NULL;
}

The search function shown above recursively moves down the tree until it either reaches a node with a key value equal to the value for which the function is searching or until the function reaches an uninitialized node, meaning that the value being searched for is not stored in the binary tree. It returns a pointer to the node to the previous instance of the function which called it, handing the pointer back up to the search function accessible outside the class.

void btree::insert(int key)
{
  if(root!=NULL)
    insert(key, root);
  else
  {
    root=new node;
    root->key_value=key;
    root->left=NULL;
    root->right=NULL;
  }
}

The public version of the insert function takes care of the case where the root has not been initialized by allocating the memory for it and setting both child nodes to NULL and setting the key_value to the value to be inserted. If the root node already exists, insert is called with the root node as the initial node of the function, and the recursive insert function takes over.

node *btree::search(int key)
{
  return search(key, root);
}

The public version of the search function is used to set off the search recursion at the root node, keeping it from being necessary for the user to have access to the root node.

void btree::destroy_tree()
{
  destroy_tree(root);
}

For more details about this check spring web hosting website.

Lesson 17: Functions with Variable Argument Lists in C and C++ using va_list

Perhaps you would like to have a function that will accept any number of values and then return the average. You don’t know how many arguments will be passed in to the function. One way you could make the function would be to accept a pointer to an array. Another way would be to write a function that can take any number of arguments. So you could write avg(4, 12.2, 23.3, 33.3, 12.1); or you could write avg(2, 2.3, 34.4); Some library functions can accept a variable list of arguments (such as the venerable printf).

To use a function with variable number of arguments, or more precisely, a function without a set number of arguments, you would use the cstdarg header file. There are four parts needed: va_list, which stores the list of arguments, va_start, which initializes the list, va_arg, which returns the next argument in the list, and va_end, which cleans up the variable argument list. Whenever a function is declared to have an indeterminate number of arguments, in place of the last argument you should place an ellipsis (which looks like ‘…’), so, int a_function ( int x, … ); would tell the compiler the function should accept however many arguments that the programmer uses, as long as it is equal to at least one, the one being the first, x.

va_list is like any other variable. For example,

va_list a_list;

va_start is a macro which accepts two arguments, a va_list and the name of the variable that directly precedes the ellipsis (…). So, in the function a_function, to initialize a_list with va_start, you would write va_start ( a_list, x );

va_arg takes a va_list and a variable type, and returns the next argument in the list in the form of whatever variable type it is told. It then moves down the list to the next argument. For example, va_arg ( a_list, double ) will return the next argument, assuming it exists, in the form of a double. The next time it is called, it will return the argument following the last returned number, if one exists.

To show how each of the parts works, take an example function:

#include <cstdarg>
#include <iostream>

using namespace std;

// this function will take the number of values to average
// followed by all of the numbers to average
double average ( int num, ... )
{
  va_list arguments;                     // A place to store the list of arguments
  double sum = 0;

  va_start ( arguments, num );           // Initializing arguments to store all values after num
  for ( int x = 0; x < num; x++ )        // Loop until all numbers are added
    sum += va_arg ( arguments, double ); // Adds the next value in argument list to sum.
  va_end ( arguments );                  // Cleans up the list

  return sum / num;                      // Returns the average
}
int main()
{
    // this computes the average of 13.2, 22.3 and 4.5 (3 indicates the number of values to average)
  cout<< average ( 3, 12.2, 22.3, 4.5 ) <<endl;
    // here it computes the average of the 5 values 3.3, 2.2, 1.1, 5.5 and 3.3
  cout<< average ( 5, 3.3, 2.2, 1.1, 5.5, 3.3 ) <<endl;
}

It isn’t necessarily a good idea to use a variable argument list at all times, because the potential exists for assuming a value is of one type, while it is in fact another, such as a null pointer being assumed to be an integer. Consequently, variable argument lists should be used sparingly.

For more details about this check spring web hosting website.

Lesson 16: Recursion in C and C++

Recursion is a programming technique that allows the programmer to express operations in terms of themselves. In C++, this takes the form of a function that calls itself. A useful way to think of recursive functions is to imagine them as a process being performed where one of the instructions is to “repeat the process”. This makes it sound very similar to a loop because it repeats the same code, and in some ways it is similar to looping. On the other hand, recursion makes it easier to express ideas in which the result of the recursive call is necessary to complete the task. Of course, it must be possible for the “process” to sometimes be completed without the recursive call. One simple example is the idea of building a wall that is ten feet high; if I want to build a ten foot high wall, then I will first build a 9 foot high wall, and then add an extra foot of bricks. Conceptually, this is like saying the “build wall” function takes a height and if that height is greater than one, first calls itself to build a lower wall, and then adds one a foot of bricks.

A simple example of recursion would be:

void recurse()
{
  recurse(); //Function calls itself
}

int main()
{
  recurse(); //Sets off the recursion
}

This program will not continue forever, however. The computer keeps function calls on a stack and once too many are called without ending, the program will crash. Why not write a program to see how many times the function is called before the program terminates?

#include <iostream>

using namespace std;

void recurse ( int count ) // Each call gets its own count
{
  cout<< count <<"\n";
  // It is not necessary to increment count since each function's
  //  variables are separate (so each count will be initialized one greater)
  recurse ( count + 1 );
}

int main()
{
  recurse ( 1 ); //First function call, so it starts at one        
}

This simple program will show the number of times the recurse function has been called by initializing each individual function call’s count variable one greater than it was previous by passing in count + 1. Keep in mind, it is not a function restarting itself, it is hundreds of functions that are each unfinished with the last one calling a new recurse function.

It can be thought of like the Russian dolls that always have a smaller doll inside. Each doll calls another doll, and you can think of the size being a counter variable that is being decremented by one.

Think of a really tiny doll, the size of a few atoms. You can’t get any smaller than that, so there are no more dolls. Normally, a recursive function will have a variable that performs a similar action; one that controls when the function will finally exit. The condition where the function will not call itself is termed the base case of the function. Basically, it is an if-statement that checks some variable for a condition (such as a number being less than zero, or greater than some other number) and if that condition is true, it will not allow the function to call itself again. (Or, it could check if a certain condition is true and only then allow the function to call itself).

A quick example:

void doll ( int size )
{
  if ( size == 0 )   // No doll can be smaller than 1 atom (10^0==1) so doesn't call itself
    return;          // Return does not have to return something, it can be used
                     //  to exit a function
  doll ( size - 1 ); // Decrements the size variable so the next doll will be smaller.
}
int main()
{
  doll ( 10 ); //Starts off with a large doll (it's a logarithmic scale)
}

This program ends when size equals one. This is a good base case, but if it is not properly set up, it is possible to have an base case that is always true (or always false).

Once a function has called itself, it will be ready to go to the next line after the call. It can still perform operations. One function you could write could print out the numbers 123456789987654321. How can you use recursion to write a function to do this? Simply have it keep incrementing a variable passed in, and then output the variable…twice, once before the function recurses, and once after…

void printnum ( int begin )
{
  cout<< begin;
  if ( begin < 9 )         // The base case is when begin is greater than 9
  {                           //  for it will not recurse after the if-statement
      printnum ( begin + 1 ); 
  }
  cout<< begin;         // Outputs the second begin, after the program has
                              //  gone through and output
}

This function works because it will go through and print the numbers begin to 9, and then as each printnum function terminates it will continue printing the value of begin in each function from 9 to begin.

This is just the beginning of the usefulness of recursion. Here’s a little challenge, use recursion to write a program that returns the factorial of any number greater than 0. (Factorial is number * (number – 1) * (number – 2) … * 1).

Hint: Recursively find the factorial of the smaller numbers first, i.e., it takes a number, finds the factorial of the previous number, and multiplies the number times that factorial…have fun. :-)

For more details about this check spring web hosting website.

Lesson 15: Singly linked lists in C++

Linked lists are a way to store data with structures so that the programmer can automatically create a new place to store data whenever necessary. Specifically, the programmer writes a struct or class definition that contains variables holding information about something, and then has a pointer to a struct of its type. Each of these individual struct or classes in the list is commonly known as a node.

Think of it like a train. The programmer always stores the first node of the list. This would be the engine of the train. The pointer is the connector between cars of the train. Every time the train adds a car, it uses the connectors to add a new car. This is like a programmer using the keyword new to create a pointer to a new struct or class.

In memory it is often described as looking like this:

----------        ----------
- Data   -        - Data   -    
----------        ----------   
- Pointer- - - -> - Pointer-  
----------        ----------

The representation isn’t completely accurate, but it will suffice for our purposes. Each of the big blocks is a struct (or class) that has a pointer to another one. Remember that the pointer only stores the memory location of something, it is not that thing, so the arrow goes to the next one. At the end, there is nothing for the pointer to point to, so it does not point to anything, it should be a null pointer or a dummy node to prevent it from accidentally pointing to a totally arbitrary and random location in memory (which is very bad).

So far we know what the node struct should look like:

struct node {
  int x;
  node *next;
};

int main()
{
  node *root;      // This will be the unchanging first node

  root = new node; // Now root points to a node struct
  root->next = 0;  // The node root points to has its next pointer
                   //  set equal to a null pointer
  root->x = 5;     // By using the -> operator, you can modify the node
                   //  a pointer (root in this case) points to.
}

This so far is not very useful for doing anything. It is necessary to understand how to traverse (go through) the linked list before going further.

Think back to the train. Lets imagine a conductor who can only enter the train through the engine, and can walk through the train down the line as long as the connector connects to another car. This is how the program will traverse the linked list. The conductor will be a pointer to node, and it will first point to root, and then, if the root’s pointer to the next node is pointing to something, the “conductor” (not a technical term) will be set to point to the next node. In this fashion, the list can be traversed. Now, as long as there is a pointer to something, the traversal will continue. Once it reaches a null pointer (or dummy node), meaning there are no more nodes (train cars) then it will be at the end of the list, and a new node can subsequently be added if so desired.

Here’s what that looks like:

struct node {
  int x;
  node *next;
};

int main()
{
  node *root;       // This won't change, or we would lose the list in memory
  node *conductor;  // This will point to each node as it traverses the list

  root = new node;  // Sets it to actually point to something
  root->next = 0;   //  Otherwise it would not work well
  root->x = 12;
  conductor = root; // The conductor points to the first node
  if ( conductor != 0 ) {
    while ( conductor->next != 0)
      conductor = conductor->next;
  }
  conductor->next = new node;  // Creates a node at the end of the list
  conductor = conductor->next; // Points to that node
  conductor->next = 0;         // Prevents it from going any further
  conductor->x = 42;
}

That is the basic code for traversing a list. The if statement ensures that there is something to begin with (a first node). In the example it will always be so, but if it was changed, it might not be true. If the if statement is true, then it is okay to try and access the node pointed to by conductor. The while loop will continue as long as there is another pointer in the next. The conductor simply moves along. It changes what it points to by getting the address of conductor->next.

Finally, the code at the end can be used to add a new node to the end. Once the while loop as finished, the conductor will point to the last node in the array. (Remember the conductor of the train will move on until there is nothing to move on to? It works the same way in the while loop.) Therefore, conductor->next is set to null, so it is okay to allocate a new area of memory for it to point to. Then the conductor traverses one more element (like a train conductor moving on to the newly added car) and makes sure that it has its pointer to next set to 0 so that the list has an end. The 0 functions like a period, it means there is no more beyond. Finally, the new node has its x value set. (It can be set through user input. I simply wrote in the ‘=42′ as an example.)

To print a linked list, the traversal function is almost the same. It is necessary to ensure that the last element is printed after the while loop terminates.

For example:

conductor = root;
if ( conductor != 0 ) { //Makes sure there is a place to start
  while ( conductor->next != 0 ) {
    cout<< conductor->x;
    conductor = conductor->next;
  }
  cout<< conductor->x;
}

The final output is necessary because the while loop will not run once it reaches the last node, but it will still be necessary to output the contents of the next node. Consequently, the last output deals with this. Because we have a pointer to the beginning of the list (root), we can avoid this redundancy by allowing the conductor to walk off of the back of the train. Bad for the conductor (if it were a real person), but the code is simpler as it also allows us to remove the initial check for null (if root is null, then conductor will be immediately set to null and the loop will never begin):

conductor = root;
while ( conductor != NULL ) {
  cout<< conductor->x;
  conductor = conductor->next;
}

For more details about this check spring web hosting website.

Lesson 14: Accepting command line arguments in C++ using argc and argv

In C++ it is possible to accept command line arguments. Command-line arguments are given after the name of a program in command-line operating systems like DOS or Linux, and are passed in to the program from the operating system. To use command line arguments in your program, you must first understand the full declaration of the main function, which previously has accepted no arguments. In fact, main can actually accept two arguments: one argument is number of command line arguments, and the other argument is a full list of all of the command line arguments.

The full declaration of main looks like this:

int main ( int argc, char *argv[] )

The integer, argc is the ARGument Count (hence argc). It is the number of arguments passed into the program from the command line, including the name of the program.

The array of character pointers is the listing of all the arguments. argv[0] is the name of the program, or an empty string if the name is not available. After that, every element number less than argc is a command line argument. You can use each argv element just like a string, or use argv as a two dimensional array. argv[argc] is a null pointer.

How could this be used? Almost any program that wants its parameters to be set when it is executed would use this. One common use is to write a function that takes the name of a file and outputs the entire text of it onto the screen.

#include <fstream>
#include <iostream>

using namespace std;

int main ( int argc, char *argv[] )
{
  if ( argc != 2 ) // argc should be 2 for correct execution
    // We print argv[0] assuming it is the program name
    cout<<"usage: "<< argv[0] <<" <filename>\n";
  else {
    // We assume argv[1] is a filename to open
    ifstream the_file ( argv[1] );
    // Always check to see if file opening succeeded
    if ( !the_file.is_open() )
      cout<<"Could not open file\n";
    else {
      char x;
      // the_file.get ( x ) returns false if the end of the file
      //  is reached or an error occurs
      while ( the_file.get ( x ) )
        cout<< x;
    }
    // the_file is closed implicitly here
  }
}

This program is fairly simple. It incorporates the full version of main. Then it first checks to ensure the user added the second argument, theoretically a file name. The program then checks to see if the file is valid by trying to open it. This is a standard operation that is effective and easy. If the file is valid, it gets opened in the process. The code is self-explanatory, but is littered with comments, you should have no trouble understanding its operation this far into the tutorial. :-)

For more details about this check spring web hosting website.

Lesson 13: Inline Functions in C++

Although you’ve already learned about basic functions in c++, there is more: the inline function. Inline functions are not always important, but it is good to understand them. The basic idea is to save time at a cost in space. Inline functions are a lot like a placeholder. Once you define an inline function, using the ‘inline’ keyword, whenever you call that function the compiler will replace the function call with the actual code from the function.

How does this make the program go faster? Simple, function calls are simply more time consuming than writing all of the code without functions. To go through your program and replace a function you have used 100 times with the code from the function would be time consuming not too bright. Of course, by using the inline function to replace the function calls with code you will also greatly increase the size of your program.

Using the inline keyword is simple, just put it before the name of a function. Then, when you use that function, pretend it is a non-inline function.

Example Inline Function

 

#include <iostream>

using namespace std;

inline void hello()
{ 
  cout<<"hello";
}
int main()
{
  hello(); //Call it like a normal function...
  cin.get();
}

However, once the program is compiled, the call to hello(); will be replaced by the code making up the function.

A WORD OF WARNING: Inline functions are very good for saving time, but if you use them too often or with large functions you will have a tremendously large program. Sometimes large programs are actually less efficient, and therefore they will run more slowly than before. Inline functions are best for small functions that are called often.

Finally, note that the compiler may choose, in its infinite wisdom, to ignore your attempt to inline a function. So if you do make a mistake and inline a monster fifty-line function that gets called thousands of times, the compiler may ignore you.

In the future, we will discuss inline functions in terms of C++ classes. Now that you understand the concept I will feel more comfortable using inline functions in later tutorials.

For more details about this check spring web hosting website.

Lesson 12: Introduction to Classes in C++

C++ is a bunch of small additions to C, with a few major additions. One major addition is the object-oriented approach (the other addition is support for generic programming, which we’ll cover later). As the name object-oriented programming suggests, this approach deals with objects. Of course, these are not real-life objects themselves. Instead, these objects are the essential definitions of real world objects. Classes are collections of data related to a single object type. Classes not only include information regarding the real world object, but also functions to access the data, and classes possess the ability to inherit from other classes. (Inheritance is covered in a later lesson.)

If a class is a house, then the functions will be the doors and the variables will be the items inside the house. The functions usually will be the only way to modify the variables in this structure, and they are usually the only way even to access the variables in this structure. This might seem silly at first, but the idea to make programs more modular – the principle itself is called “encapsulation”. The key idea is that the outside world doesn’t need to know exactly what data is stored inside the class–it just needs to know which functions it can use to access that data. This allows the implementation to change more easily because nobody should have to rely on it except the class itself.

The syntax for these classes is simple. First, you put the keyword ‘class’ then the name of the class. Our example will use the name Computer. Then you put an open bracket. Before putting down the different variables, it is necessary to put the degree of restriction on the variable. There are three levels of restriction. The first is public, the second protected, and the third private. For now, all you need to know is that the public restriction allows any part of the program, including parts outside the class, to access the functions and variables specified as public. The protected restriction prevents functions outside the class to access the variable. The private restriction is similar to protected (we’ll see the difference later when we look at inheritance. The syntax for declaring these access restrictions is merely the restriction keyword (public, private, protected) and then a colon. Finally, you put the different variables and functions (You usually will only put the function prototype[s]) you want to be part of the class. Then you put a closing bracket and semicolon. Keep in mind that you still must end the function prototype(s) with a semi-colon.

Let’s look at these different access restrictions for a moment. Why would you want to declare something private instead of public? The idea is that some parts of the class are intended to be internal to the class–only for the purpose of implementing features. On the other hand, some parts of the class are supposed to be available to anyone using the class–these are the public class functions. Think of a class as though it were an appliance like a microwave: the public parts of the class correspond to the parts of the microwave that you can use on an everyday basis–the keypad, the start button, and so forth. On the other hand, some parts of the microwave are not easily accessible, but they are no less important–it would be hard to get at the microwave generator. These would correspond to the protected or private parts of the class–the things that are necessary for the class to function, but that nobody who uses the class should need to know about. The great thing about this separation is that it makes the class easier to use (who would want to use a microwave where you had to know exactly how it works in order to use it?) The key idea is to separate the interface you use from the way the interface is supported and implemented.

Classes must always contain two functions: a constructor and a destructor. The syntax for them is simple: the class name denotes a constructor, a ~ before the class name is a destructor. The basic idea is to have the constructor initialize variables, and to have the destructor clean up after the class, which includes freeing any memory allocated. If it turns out that you don’t need to actually perform any initialization, then you can allow the compiler to create a “default constructor” for you. Similarly, if you don’t need to do anything special in the destructor, the compiler can write it for you too!

When the programmer declares an instance of the class, the constructor will be automatically called. The only time the destructor is called is when the instance of the class is no longer needed–either when the program ends, the class reaches the end of scope, or when its memory is deallocated using delete (if you don’t understand all of that, don’t worry; the key idea is that destructors are always called when the class is no longer usable). Keep in mind that neither constructors nor destructors return arguments! This means you do not want to (and cannot) return a value in them.

Note that you generally want your constructor and destructor to be made public so that your class can be created! The constructor is called when an object is created, but if the constructor is private, it cannot be called so the object cannot be constructed. This will cause the compiler to complain.

The syntax for defining a function that is a member of a class outside of the actual class definition is to put the return type, then put the class name, two colons, and then the function name. This tells the compiler that the function is a member of that class.

For example:

#include <iostream>

using namespace std;

class Computer // Standard way of defining the class
{
public:
  // This means that all of the functions below this(and any variables)
  //  are accessible to the rest of the program.
  //  NOTE: That is a colon, NOT a semicolon...
  Computer();
  // Constructor
  ~Computer();
  // Destructor
  void setspeed ( int p );
  int readspeed();
protected:
  // This means that all the variables under this, until a new type of
  //  restriction is placed, will only be accessible to other functions in the
  //  class.  NOTE: That is a colon, NOT a semicolon...
  int processorspeed;
};
// Do Not forget the trailing semi-colon

Computer::Computer()
{
  //Constructors can accept arguments, but this one does not
  processorspeed = 0;
}

Computer::~Computer()
{
  //Destructors do not accept arguments
}

void Computer::setspeed ( int p )
{
  // To define a function outside put the name of the class
  //  after the return type and then two colons, and then the name
  //  of the function.
  processorspeed = p;
}
int Computer::readspeed()  
{
  // The two colons simply tell the compiler that the function is part
  //  of the class
  return processorspeed;
}

int main()
{
  Computer compute;  
  // To create an 'instance' of the class, simply treat it like you would
  //  a structure.  (An instance is simply when you create an actual object
  //  from the class, as opposed to having the definition of the class)
  compute.setspeed ( 100 ); 
  // To call functions in the class, you put the name of the instance,
  //  a period, and then the function name.
  cout<< compute.readspeed();
  // See above note.
}

For more details about this check spring web hosting website.

Lesson 11: Typecasting in C and C++

Typecasting is making a variable of one type, such as an int, act like another type, a char, for one single operation. To typecast something, simply put the type of variable you want the actual variable to act as inside parentheses in front of the actual variable. (char)a will make ‘a’ function as a char.

For example:

#include <iostream> 

using namespace std;

int main()       
{
  cout<< (char)65 <<"\n"; 
  // The (char) is a typecast, telling the computer to interpret the 65 as a
  //  character, not as a number.  It is going to give the character output of 
  //  the equivalent of the number 65 (It should be the letter A for ASCII).
  cin.get();
}

One use for typecasting for is when you want to use the ASCII characters. For example, what if you want to create your own chart of all 128 ASCII characters. To do this, you will need to use to typecast to allow you to print out the integer as its character equivalent.

#include <iostream>

using namespace std;

int main()
{
  for ( int x = 0; x < 128; x++ ) {
    cout<< x <<". "<< (char)x <<" "; 
    //Note the use of the int version of x to 
    // output a number and the use of (char) to 
    // typecast the x into a character 	
    // which outputs the ASCII character that 
    // corresponds to the current number
  }
  cin.get();
}

The typecast described above is a C-style cast, C++ supports two other types. First is the function-style cast:

int main()       
{
  cout<< char ( 65 ) <<"\n"; 
  cin.get();
}

This is more like a function call than a cast as the type to be cast to is like the name of the function and the value to be cast is like the argument to the function. Next is the named cast, of which there are four:

int main()       
{
  cout<< static_cast<char> ( 65 ) <<"\n"; 
  cin.get();
}

static_cast is similar in function to the other casts described above, but the name makes it easier to spot and less tempting to use since it tends to be ugly. Typecasting should be avoided whenever possible. The other three types of named casts are const_cast, reinterpret_cast, and dynamic_cast. They are of no use to us at this time.

Typecasts in practice

So when exactly would a typecast come in handy? One use of typecasts is to force the correct type of mathematical operation to take place. It turns out that in C and C++ (and other programming languages), the result of the division of integers is itself treated as an integer: for instance, 3/5 becomes 0! Why? Well, 3/5 is less than 1, and integer division ignores the remainder.

On the other hand, it turns out that division between floating point numbers, or even between one floating point number and an integer, is sufficient to keep the result as a floating point number. So if we were performing some kind of fancy division where we didn’t want truncated values, we’d have to cast one of the variables to a floating point type. For instance, static_cast<float>(3)/5 comes out to .6, as you would expect!

When might this come up? It’s often reasonable to store two values in integers. For instance, if you were tracking heart patients, you might have a function to compute their age in years and the number of heart times they’d come in for heart pain. One operation you might conceivably want to perform is to compute the number of times per year of life someone has come in to see their physician about heart pain. What would this look like?

/* magical function returns the age in years */
int age = getAge();  
/* magical function returns the number of visits */
int pain_visits = getVisits(); 

float visits_per_year = pain_visits / age;

The problem is that when this program is run, visits_per_year will be zero unless the patient had an awful lot of visits to the doc. The way to get around this problem is to cast one of the values being divided so it gets treated as a floating point number, which will cause the compiler to treat the expression as if it were to result in a floating point number:

float visits_per_year = pain_visits / static_cast<float>(age);
/* or */
float visits_per_year = static_cast<float>(pain_visits) / age;

This would cause the correct values to be stored in visits_per_year. Can you think of another solution to this problem (in this case)?

For more details about this check spring web hosting website.

Lesson 10: C++ File I/O

This is a slightly more advanced topic than what I have covered so far, but I think that it is useful. File I/O is reading from and writing to files. This lesson will only cover text files, that is, files that are composed only of ASCII text.

C++ has two basic classes to handle files, ifstream and ofstream. To use them, include the header file fstream. Ifstream handles file input (reading from files), and ofstream handles file output (writing to files). The way to declare an instance of the ifstream or ofstream class is:

ifstream a_file;

or

ifstream a_file ( "filename" );

The constructor for both classes will actually open the file if you pass the name as an argument. As well, both classes have an open command (a_file.open()) and a close command (a_file.close()). You aren’t required to use the close command as it will automatically be called when the program terminates, but if you need to close the file long before the program ends, it is useful.

The beauty of the C++ method of handling files rests in the simplicity of the actual functions used in basic input and output operations. Because C++ supports overloading operators, it is possible to use << and >> in front of the instance of the class as if it were cout or cin. In fact, file streams can be used exactly the same as cout and cin after they are opened.

For example:

#include <fstream>
#include <iostream>

using namespace std;

int main()
{
  char str[10];

  //Creates an instance of ofstream, and opens example.txt
  ofstream a_file ( "example.txt" );
  // Outputs to example.txt through a_file
  a_file<<"This text will now be inside of example.txt";
  // Close the file stream explicitly
  a_file.close();
  //Opens for reading the file
  ifstream b_file ( "example.txt" );
  //Reads one string from the file
  b_file>> str;
  //Should output 'this'
  cout<< str <<"\n";
  cin.get();    // wait for a keypress
  // b_file is closed implicitly here
}

The default mode for opening a file with ofstream’s constructor is to create it if it does not exist, or delete everything in it if something does exist in it. If necessary, you can give a second argument that specifies how the file should be handled. They are listed below:

ios::app   -- Append to the file
ios::ate   -- Set the current position to the end
ios::trunc -- Delete everything in the file

For example:

ofstream a_file ( "test.txt", ios::app );

This will open the file without destroying the current contents and allow you to append new data. When opening files, be very careful not to use them if the file could not be opened. This can be tested for very easily:

ifstream a_file ( "example.txt" );

if ( !a_file.is_open() ) {
  // The file could not be opened
}
else {
  // Safely use the file stream
}

For more details about this check spring web hosting website.