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C Constants
Definition
When you need to lock in a value so that it can’t be changed—either accidentally or intentionally—you use the const modifier. It creates a read-only variable whose content stays fixed forever once assigned.
Illustration
const int speedLimit = 80; // speedLimit is permanently set to 80 SpeedLimit = 100; // ❌ Error: speedLimit is immutable
When to Use It
Apply const when the value is permanent or represents a universal truth within your program logic.
const int HOURS_IN_DAY = 24;
Important Rule
Every constant must be immediately initialized when declared. Delayed assignment is not allowed.
Valid:
const float PI = 3.14;
Invalid:
const float PI; PI = 3.14; // ❌ Compile-time error
Style Tip
By convention, constant identifiers are written using all capital letters to make them stand out and signal their unchangeable nature.
const int MAX_USERS = 100;
This isn’t required by the compiler, but it improves clarity for people reading your code.
Summary Points
- const ensures that a variable cannot be changed after assignment.
- Constants must be initialized at declaration.
- It’s good style to use UPPERCASE names for constant variables.
- Helps prevent logic errors and maintains integrity in your program.
Prefer Learning by Watching?
Watch these YouTube tutorials to understand C Tutorial visually:
What You'll Learn:
- 📌 Constants in C (Part 1)
- 📌 C_07 Constants in C | Types of Constants | Programming in C