C Constants

 C Constants (Complete Guide: Beginner → Advanced)

In C language, a constant is a value that cannot be changed during program execution.
Constants improve code safety, readability, and maintainability, and they are very important for interviews.

 What is a Constant in C?

A constant is a fixed value whose value does not change while the program is running.

 Types of Constants in C

C constants are mainly divided into:

1. Numeric Constants

2. Character Constants

3. String Constants

4. Symbolic Constants

5. Enumeration Constants

 Numeric Constants

 Integer Constants

 Floating-Point Constants

Example

 Character Constants

A single character enclosed in single quotes.

Example:

• Stored internally as ASCII value

 String Constants

A sequence of characters enclosed in double quotes.

Example:

•  Automatically ends with '\0'

 Symbolic Constants using #define

Defined using preprocessor directive.

Syntax

Example

•  No memory allocation
•  No type checking

 Constants using const Keyword (Recommended)

Syntax

Example

•  Type safe
•  Preferred over #define

 Difference: #define vs const

 Enumeration Constants (enum)

Used for named integer constants.

Values:

•  Improves readability
•  Used in real projects

const with Pointers (Interview Favorite)

•  Very important for advanced interviews

 Common Mistakes

•  Trying to modify a constant
•  Confusing const int *p with int *const p
•  Overusing #define 
•  Forgetting string '\0'

 Interview Questions (Must Prepare)

1. What is a constant in C?

2. Difference between #define and const

3. What are symbolic constants?

4. What is enum?

5. Explain const with pointer

6. Are constants stored in memory?

Real-Life Use Cases

• Mathematical values (PI, GRAVITY)

• Configuration values

• Array size limits

• Status codes

• Embedded systems

 Summary

•  Constants store fixed values
•  Use const for type safety
• #define is preprocessor-based
• enum for grouped constants
•  Very important for clean code & interviews