Functions in C

3. Functions in C

Functions are a very useful technique in very programming language. Functions are a part of a program, but coded as a separate segment. Hence they are otherwise known as subroutines.

• Modules in C

•         C standard library has a wide variety of functions

•         Ex:  x = pow(4,2) ?

•   Programs combine user-defined functions with library functions

Functions, in short modularize a program

3.1 Benefits of functions

• Divide and conquer

               Manageable program development

• Software reusability

•         Use existing functions as building blocks for new programs

•         Abstraction - hide internal details (library functions)

•  Avoid code repetition

    3.2 More on Functions 

¢     A fragment of code that accepts zero or more argument values, produces a result value, and has zero or more side effects.

¢     A method of grouping a subset of a program

•         To hide details

•         To be invoked from multiple places

•         To share with others

¢     Format for calling functions

FunctionName( argument );

•         Ex: sqrt( 9 )

•         If multiple arguments, use comma-separated list

3.3 Function definition format

The syntax for defining a function is:

return-value-type  function-name( parameter-list )
{
   declarations and statements
} 

It must noted here that,

¢     Function-name: any valid identifier

¢     Return-value-type: data type of the result (default int)

void – indicates that the function returns nothing

¢     Parameter-list: comma separated list, declares parameters

Declarations and statements: function body (block)

•         Variables can be declared inside blocks

•         Functions can not be defined inside other functions

Returning control

•         If nothing returned

•       return;

•       or, until reaches right brace

•         If something returned

•       return expression;

Question 1?

Write a program to find factorial of a number n?

main() {

int n,f=0;

printf(“Enter a number”):

scanf(“%d”,&n);

f=myfactorial(n);

printf(“ The factorial is %d”,f);

}

More on built-in functions