Constants in C

In C programming language, a constant is a value that cannot be altered during the execution of the program. Constants can be used to define fixed values that are used repeatedly in a program. In this article, we will discuss constants in C, their types, and how to declare and use them in a program.

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Constants in C

Constants in C are values that cannot be modified during the execution of a program. They are typically defined using the const keyword.

Types of Constants:

1. Literal Constants: These are directly written values within the code, such as numbers, characters, or strings.

   • Integer literals: 10, -5, 0x123 (hexadecimal), 0b101 (binary), 012 (octal)
   • Floating-point literals: 3.14, 1.2e5 (scientific notation)
   • Character literals: 'A', '\n' (newline), '\t' (tab)
   • String literals: "Hello, world!"

2. Symbolic Constants: These are named constants defined using the #define preprocessor directive.

• #define PI 3.14159

Example:

#define MAX_LENGTH 100

int main() {
    const int age = 25;
    char name[MAX_LENGTH] = "Alice";

    // You cannot modify age or MAX_LENGTH
    // age = 30; // Error
    // MAX_LENGTH = 200; // Error

    printf("Name: %s, Age: %d\n", name, age);

    return 0;
}

Advantages of Using Constants:

• Readability: Constants make code more readable by giving meaningful names to values.
• Maintainability: If you need to change a constant value, you only need to modify its definition, reducing the chances of errors.
• Efficiency: In some cases, the compiler can optimize code based on constant values, improving performance.

Best Practices:

• Use uppercase names for symbolic constants to distinguish them from variables.
• Use meaningful names that clearly indicate the purpose of the constant.
• Avoid modifying constants during runtime.