Q.What is function?

A function is a named, self-contained block of statements that performs a specific task. C is fundamentally a language of functions: every program is a collection of functions, and execution always begins with the special function main().

Functions bring three big advantages. They allow modularity - a large problem is broken into smaller, manageable pieces; they support reusability - a task written once can be called many times from different places; and they make a program easier to read, test and debug.

C offers two kinds of functions:

1. Library (built-in) functions - ready-made functions supplied with C, whose declarations live in header files. For example printf() and scanf() come from stdio.h, mathematical functions such as sqrt() from math.h, string functions from string.h, and console functions such as clrscr() and getch() from conio.h. A program includes the appropriate header with #include before using such functions.
2. User-defined functions - functions written by the programmer to carry out particular tasks.

To use a function you call it by name, optionally passing values (arguments) to it; it does its work and may return a result. Understanding what a function is, why C relies on them, and the role of header files in providing library functions is a recurring short-answer topic in the II PUC Electronics course.