This document explains the concept of variables in C programming, emphasizing their need to store values in memory locations. It outlines the rules for defining variables and identifies common C libraries and their associated header files. The document lists various predefined functions available within these libraries.

1. What is a Variable ?

2. Memory is in form of blocks
128
254
512 556
1024 1248
1455 2048
206

3. Memory is in form of blocks
Suppose, we need to
store 10 in the memory 10
Stored in any
random location
Note-: We cannot access this value
10 in future because we don’t have
any location for this

4. a
Stored in this
location
a=10
printf(a)
Syntax-: data_type variable_name;
So, We Need Variables
Example-: int a;

5. Rules for defining a variable or identifier in C
• Variable must begin with a letter or an underscore.
• Variable can contain digits but not start with a digit.
• No special character is allowed to use other that underscore.
• Keywords cannot be used as a variable name.

6. What is in C library ?
Library is a collection of header files
stdio.h conio.h string.h
graphics.h math.h dos.h
Library
Header
Files
printf()
scanf()
clrscr()
getch()
strlen()
strrev()
setcolor()
setbkcolor()
rand()
pow()
getdate()
gettime()

7. Header files is the collection of related predefined
functions and C library is collection of header files