Constants in C | Set 2

Prerequisite – Constants in C
Constants refer to fixed values that the program may not alter during its execution. These fixed values are also called literals. Constants can be of any of the basic data types.

Types of Constant in C :

C supports several types of constants in C language as

1. Character Constants, i.e., Single Character Constant, and String Constant.
2. Numeric Constants :
   • Integer Constant, i.e., Decimal Integer constant, Octal integer constant, and Hexadecimal Integer constant.
   • Real Constant
3. Backslash Character constants
4. Symbolic constants

Defining Constants :

There are two simple ways in C to define constants − Using #define preprocessor, and Using const keyword.

1. Using #define preprocessor directive –
   Given below is the form to use #define preprocessor to define a constant −

   #define identifierName value 

   • identifierName : It is the name given to constant.
   • value : This refers to any value assigned to identifierName.

   Example :

   #include <stdio.h>
    
   #define LENGTH 100   
   #define WIDTH  50
   #define NEWLINE '\n'
    
   int main() {
      int area;  
    
      //test these values 
      printf("Value of LENGTH is %d", LENGTH);
      printf("%c", NEWLINE);
      printf("Value of WIDTH is %d", WIDTH);
      printf("%c", NEWLINE);
   
      //check using calculation 
      area = LENGTH * WIDTH;
      printf("Value of area is %d", area);
    
      return 0;
   }
   

   Output :

   Value of LENGTH is 100
   Value of WIDTH is 50
   Value of area is 5000 

2. Using const Keyword :
   You can use const prefix to declare constants with a specific type as follows −

   const type variable = value; 

   Example :

   #include <stdio.h>
   
   int main() {
   
      
   
      const int  LENGTH = 100;
      const int  WIDTH = 50;
      const char NEWLINE = '\n';
      
      //test these values 
      printf("Value of LENGTH is %d", LENGTH);
      printf("%c", NEWLINE);
      printf("Value of WIDTH is %d", WIDTH);
      printf("%c", NEWLINE);
      
      //check using calculation
      int area;  
      area = LENGTH * WIDTH;
      printf("value of area is %d", area);
      printf("%c", NEWLINE);
   
      return 0;
   }
   

   Output :

   Value of LENGTH is 100
   Value of WIDTH is 50
   value of area is 5000 

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