Functions

A function is a block of code that performs a specific task. In C++, we can divide a large program into the basic building blocks known as function.

A function can be called multiple times to provide reusability and modularity to the C++ program.

Reusability is the main achievement of C++ functions. By using functions, we can avoid rewriting same logic/code again and again in a program.

There are two types of functions in C programming:

      •      Library Functions: are the functions which are declared in the C++ header files

•     User-defined functions: are the functions which are created by the C++ programmer. It reduces the complexity of a big program and optimizes the code.

 

A function will have three aspects

1. Function Declaration / function prototype

2. Function Call

3. Function Definition.

 

1. Function Declaration / function prototype:

A function must be declared in a C++ program to tell the compiler about the function name, function parameters, and return type.

A function prototype is simply the declaration of a function that specifies function's name, parameters and return type. It doesn't contain function body.

Syntax of function prototype

returnType      functionName(type1 argument1, type2 argument2, ...);

Ex:

void     sum(int   x, int   y);

The function prototype is not needed if the user-defined function is defined before the main() function.

2. Function call: 

Function can be called from anywhere in the program. Control of the program is transferred to the user-defined function by calling it.

Syntax of function call

functionName(argument1, argument2, ...);

Ex:

sum(a,b);

3. Function definition:

Function definition contains the block of code to perform a specific task. When a function is called, the control of the program is transferred to the function definition. And, the compiler starts executing the codes inside the body of a function.

Syntax of function definition

returnType    functionName(type1 argument1, type2 argument2, ...)

{

    //body of the function

}

 

Ex:

void    sum(int x, int  y)

{

int  sum=x+y;

cout<<“ sum is”<< sum;

}

 

Different aspects of function calling

There are four different aspects of function calls:

 

•      function without arguments and without return value

                         Ex: void sum( );

 

•      function without arguments and with return value

                         Ex: int sum( );

 

•      function with arguments and without return value

                         void   sum(int a,int b);

 

•      function with arguments and with return value

                         int   sum(int a,int  b);