Variables in C

Variables in C Language: A variable in C language defines the what type of data it can be stored in the memory. And we can also change the value of a variable during execution of a program. It is a way to represent memory location through a symbol so that it can be easily identified.

Syntax: type variable_list;

C Variables

Example: average, name, height, employee, etc.,

extern int a, b; 
extern int c; 
int main() { 
int a, b; 
a = 7; b = 14; 
c = a + b; 
printf("Sum is : %d \n", c);  
return 0; 

Output: Sum is: 21

Datatype of Variable

Variables can store different types of data which can hold. They are like char, int, float, double, void.

Rules to name variables: 

  • A variable name must not start with a digit.    
  • It can consist of alphabets, digits and special symbols like underscore _    
  • Space and blanks are not allowed in variables.    
  • Keywords are not allowed as a variable name.    
  • Upper & lower case names are treated as different because C is case sensitive, so keep it in the lower case.   

Variable Definition in C

It defines the compiler how much memory has to be stored. And the variable definition defines a specific data type and contains a list of one or more variables of that type.

Syntax: type variable_list 


int i, j, k; 
char c,ch; 
float f, 
double d;

Rules for defining variables

  • Variable can have alphabets, digits, and underscore.
  • Variable name can start with the alphabet, and underscore only. It can’t start with a digit.
  • No whitespace is allowed within the variable name.
  • A variable name must not be any reserved word or keyword, e.g. int, float, etc.

Declaring, Defining and Initializing a Variable in C

Deceleration must be done before they are used in the program. While declaring you should know some things regarding this.

  • Deceleration tells the compiler what the variable name is.
  • It specifies what type of data the variable will holds.
  • A variable is declared using the extern keyword, outside the main () function.


extern int a, b;/*Variable declaration:*/ 
extern int c; 
extern float f; 
int main () { 
int a, b;/*Variable declaration:*/ 
int c; 
float f; 
a = 10; b = 20; 
c = a + b;
printf("value of c : %d \n", c); 
printf("value of f : %f \n", f); 
return 0; }

value of c: 30
value of f: 23.333334

L values and R values in C

There are two types of conditions in C i.e. L value and Rvalue.


lvalueExpressions which are referred to a memory location are called “lvalue” expressions. lvalue may disappear as either the left-hand or right-hand side of an assignment


rvalue refers to the data value that is stored at some address in memory.  And rvalue is an expression that cannot have a value assigned to it means an rvalue may appear on the right-hand side but not on the left-hand side of an assignment.


int g = 15;//valid statement 
20 = 30; // invalid statement; would generate compile-time error