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Your very first C++ Program


All the example programs in this book have been tested in Turbo C++ compiler (the programs were also tested in Visual C++ 6.0). They should run on other C++ compilers as well.

Let us start with a basic C++ program. This will give you an idea about the general structure of a C++ program. Let’s write a program in which the user can enter a character and the program will display the character that was typed:

      // My first C++ program

      # include <iostream.h>
      int main( )
      {

          char letter;
          cout << "Enter any letter" ;
          cin >>letter;
          cout << "The letter you entered is : " <<letter;
          return 0;

                    }

 

Explanation for the above program:

You might have noticed in the above program that every statement is terminated with a semi-colon (;). That is exactly the use of the semi-colon. It is used to tell the compiler that one instruction line is over. If you don’t put semi-colons in your program, you will get errors while compiling.

A variable is used for temporary storage of some data in a program. In the above example, ‘letter’ was a variable. Every variable belongs to a particular type (referred to as data type). The different data types in C++ are discussed later. In the above program:

char letter;

declares ‘letter’ as a character variable (a character is one of the basic data types in C++). When the compiler encounters this statement, it will allocate some memory space for this variable (i.e. any value which is assigned to the variable ‘letter’ will be stored in this allocated memory location). When the required memory space has been allocated we say that the variable has been defined (in this case a single statement will declare and define the variable ‘letter’).


Some points to remember:

When we want to display something on the screen we will code it as:

cout<<variable-name;

When we want to obtain a value for a variable from the user we will say:

cin>>variable-name;

Beware of the direction of the >> and << operators. In the statement

cout<<variable;

information flows from the variable into ‘cout’ (which means it goes to the monitor display). When we say

cin>>variable;

information (the value of the variable) flows from ‘cin’ (which would be the keyboard) into the variable (i.e. the value is stored in the variable). Information will flow in the direction of the arrows (<< or >>). ‘cout’ is linked to the standard display device (i.e. the monitor) while ‘cin’ is linked to the standard input device (i.e. the keyboard). Hence, you can’t use

cout>>variable;

This will cause an error while compiling. ‘cout’ and ‘cin’ are already pre-defined and so you can use them directly in your programs. 'iostream.h’ is a header file that is used to perform basic input and output operation (or general I/O like using ‘cin’ and ‘cout’).

Remember: C++ is a case-sensitive language, which means that the compiler will not consider ‘letter’, ‘LETTER’ and ‘Letter’ as the same.


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Copyright © 2004 Sethu Subramanian All rights reserved.