This document discusses C functions and their elements. It describes two categories of functions - library functions and user-defined functions. The key elements of user-defined functions are the function definition, function call, and function declaration. A function declaration specifies the return type, name, and parameters. A function definition implements the function with its name, return type, parameters, local variables, statements, and return statement. Functions can be called by using their name in a statement.

2. INTRODUCTION
• C functions can be classified into two
categories
– Library functions
– User-defined functions

3. LIBRARY FUNCTIONS
– Library functions are not required to be
written by
– printf and scanf belong to the category of
library function
– sqrt, cos, strcat, etc are some of library
functions

4. USER-DEFINED FUNCTIONS
– User-defined functions has to be developed by
the user at the time of writing a program
– A user-defined functions can later become a
part of the C program library
– main is an example of user-defined functions

5. ELEMENTS OF USER-DEFINED
FUNCTIONS
There are three elements related to functions
– Function definition
– Function call
– Function declaration
• The function definition is an independent program module that is specially
written to implement the requirements of the function.
• To use this function we need to invoke it at a required place in the program.
This is known as the function call.
• The program that calls the function is referred to as the calling program or
calling function.
• The calling program should declare any function that is to be used later in
the program. This is known as the function declaration or function prototype.

6. FUNCTION DECLARATION
A function declaration consists of four parts
– Function type (return type)
– Function name
– Parameter list
– Terminating semicolon
Syntax,
Function-type function-name (parameter list);
Example,
void display(int);

7. FUNCTION DEFINITION
A function definition, also known as function
implementation shall include the following
elements;
– Function name;
– Function type;
– List of parameters;
– Local variable declaration;
– Function statements; and
– A return statement.

8. Syntax is…..
function_type function_name(parameter list)
{
local variable declaration;
executable statement1;
executable statement2;
----------------
----------------
return(expression);
}

9. FUNCTION

10. CALLING A FUNCTION
A function can be called by simply using the
function name in a statement
When the function encounters a function call,
the control is transferred to the function
mul(x,y)

11. Example program
main()
{
int p;
p = mul(10,5);
printf("%dn", p);
}
int mul(int x,int y)
{
int p; /*local variables*/
p = x * y;/* x = 10, y = 5*/
return(p);
}

12. CATEGORY OF FUNCTIONS
Category 1: Functions with no arguments and no
return values
Category 2: Functions with arguments and no
return values
Category 3: Functions with arguments and one
return values
Category 4: Functions with no arguments but
return a value

16. Function with no arguments and with return
Values
Main() data_type func1()
{ {
………….. ……………
………….. ……………
C=func1(); ……………
………….. …………….
…………... Return(a);
}

17. RETURNING A VALUE
• C function returns a value of the type int as a
default case when no other type is specified
explicitly.
return(value);
Return the integer value of sum