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 C++ Tutorials  >  Functions  >  Need for a Funtion

Modular Approach

Functions are the building blocks of C++ programs. A function groups a number of program statements into a single unit. This unit can be invoked from other parts of the program.

Need for a Function

When programs become large, a single list of instruction becomes difficult to understand. For this reason, functions are used. A function has a cleared defined purpose and has an interface to other functions in the program. A group of functions together form a large entity called a module.

Another reason for using functions is to reduce the size of the program. Any sequence of instructions that is repeated in a program can be grouped together to form a function. The function code is stored in only one place in the memory even though the function may be executed a repeated number of times.

The following program illustrates the usage of a function:

//Program 7.1
//This program uses a function to calculate the sum of two numbers
void add();
void main()
cout<<"Calling function add()"<<endl;
add(); //A call to the function add(), while calling a function the command is terminated with a ';'
cout<<"A return from add() function"<<endl;

//Function definition for add
void add()
int iNum1, iNum2, iNum3;
iNum3 = iNum1 + iNum2;
cout<<"The sum of the two numbers is"<<iNum3<<endl;

In Program 7.1, the function add() is invoked from the function main(). The control passes to the function add(), and the body of function is executed. The control then returns to main() and the remaining code of main() is executed.

The sample output of Program 7.1 si:

Calling function add()
Input two numbers
The sum of the two numbers is 30
A return from add() function

In Program 7.1, the function main(), which invokes the function add(), is called the calling function, and the function add() is the called function.

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