A variable is a named location in memory that is used to hold a value that can be modified by the program. All variable must be declared before they can be used. The general form of a declaration is
Here, type must be a valid data type plus any modifiers, and variable_list may consist of one or more identifier names separated by commas. Here are some declarations:
int i, j, k;
short int si;
unsigned int ui;
double balance, profit, loss;
Note: In C the name of a variable has nothing to do with its type.
Where Variable Are Declared
Variable can be declared in three places: inside functions, in the definition of function parameters, and outside of all functions. These positions correspond to a local variable, formal parameters, and global variable respectively.
Variables that are declared inside a function are called local variables. In C literature, these variables are referred to as automatic variables. Local variables can be used only by statements that are inside the block in which the variables are declared. Local variables are not known outside their own code block. A block of code begins with an opening curly brace and terminates with a closing curly brace.
The local variable exists only while the block of code in which they are declared is executing. The most common code block in which local variables are declared is the function.
x =10 ;
If a function is to use arguments, it must declare variables that will accept the values of the arguments. These variables are called the formal parameters of the function. They behave like any other variables inside the function. As shown in the following program fragment, their declarations occur after the function name and inside parentheses.
if (*s==c) return1;
Global variables are known throughout the program and may be used by any piece of code. Also, they will hold their value throughout the program’s execution. We create global variables by declaring them outside of any function. Any expression may access them, regardless of what block of code that expression is in.