What are constants in C language ?

In C programming, constants are fixed values that cannot be changed during program execution. They are used to represent data that remains constant throughout the program, ensuring consistency and preventing accidental modifications.

Here are the different types of constants in C:

1. Literal Constants:

   • Values directly written into the code.
   • Types:
     • Integer literals: Whole numbers (e.g., 10, -5, 0x2A)
     • Floating-point literals: Numbers with decimals (e.g., 3.14, 1.2e-5)
     • Character literals: Single characters enclosed in single quotes (e.g., ‘A’, ‘\n’, ‘\t’)
     • String literals: Sequences of characters enclosed in double quotes (e.g., “Hello, world!”)

2. Defined Constants:

   • Created using the #define preprocessor directive.
   • Syntax:
     C

     #define CONSTANT_NAME value
     

   • Example:
     C

     #define PI 3.14159
     

3. Enumerated Constants:

   • Defined using the enum keyword.
   • Used to assign names to a set of integer constants.
   • Example:
     C

     enum Weekdays { Monday, Tuesday, Wednesday, Thursday, Friday };
     

Advantages of Constants:

• Readability: Meaningful names for fixed values enhance code clarity.
• Maintainability: Easier to update values in one place if needed.
• Reliability: Prevent accidental changes to critical values.
• Efficiency: The compiler can often optimize code using constants.

Best Practices:

• Use uppercase names for constants to distinguish them from variables (e.g., MAX_VALUE, PI).
• Consider using defined constants for values that might need adjustment later.
• Employ enumerated constants for sets of related integer values.