Every C++ program follows this basic/general structure:
[Compiler_Directives]
int main ()
{
[Local_Variable_Declarations]
[Body]
}
The following is an example program using the above structure:
/* This program calculates the product of two numbers */
// Compiler Directives
#include <iostream.h>
int main () {
// Local Variable Declaration
int
firstNumber,
secondNumber,
product;
cout << "Welcome to the Product Machine\n\n"; // Displays program title
cout << "Please enter the first number: "; // Prompts for first number
cin >> firstNumber; // Grabs first number
cout << "Please enter the second number: "; // Prompts for second number
cin >> secondNumber; // Grabs second number
product = firstNumber * secondNumber; // Calculates product
cout << "The product is " << product << "\n"; // Displays product
}
· The program begins with a comment box explaining what the program does. A comment is identified either by surrounding it with /* and */ (as in: /* this is a comment */) or by placing // at the beginning of each commented line. In the latter case, all text after // on the same line will be treated as the comment.
· Next is the compiler directive #include <iostream.h>. This statement tells the compiler to include the declarations found in iostream.h, a library which provides the capabilities needed to perform interactive I/O.
· Following this directive is the main C++ function, indicated by
int main () {
.
.
.
}
where:
· main is the name of the main C++ function. It is the first function run when a program is executed.
· the () after the function name represents the parameter types that will be accepted. If it is empty, or contains the keyword void, it does not accept anything.
· the column of dots represents the body of the program
· The body usually consists of a variable declaration area and the accompanying code. In the above example, we declared three int (integer) variables; namely, firstNumber, secondNumber, and product. Other more commonly used variables types are: double, float, and char.
· The cin/cout functions are interactive input-output (I/O) functions associated with the stream.h library and are explained further in the cin/cout tutorial page.
· Assignments to variables take the form of targetVar = Value; where targetVar must be of a matching type with Value (see tutorial on variable assignment).