C Functions

A function is a piece of code that can be used repeatedly in a C program. A function is mainly of two types:

  • Built in Functions; which are already defined in C Library.
  • User Defined Functions; which are created and defined by users.



Return_type functionName(parameters)


    code to be executed;



Rules for using Functions:

  • Void return type is used when nothing need to be returned from the function.
  • Functions can also be used to return value. Return type such as int, long, char etc. are used to return a value from the function of the given type.
  • A function starts with an opening curly brace ( { ) and ends with a closing curly brace ( } ).
  • Arguments are the variables, inside the parentheses, after the function name which is used to pass informations to functions.
  • For multiple arguments, comma should be used for separation.
  • Default argument value can also be specified in a function. If no argument is specified, the function will take the default argument.


Calling a Function in C:

In order to get the value returned from the function, the function need to be called in the program.


Variable_name = function_name (parameters_values);


int writeMsg()
printf ("My First Program using Function!");
return 0;
void main()


My First Program using Function!
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