There are Two Types of Functions in C

• predefined functions
• user defined functions

Predefined functions

• These functions are already defined in the system libraries.
• Programmer can reuse the existing code in the system libraries which is helpful to write error free code.
• User must be aware of syntax of the function.

Example: printf() , clrscr()

User defined functions

• These functions must be defined by the programmer or user.
• Programmer has to write the coding for such functions and test them properly before using them.
• The syntax of the function is given by the user so there is no need to include any header files.

Example: main(), swap(), sum(), etc..