Constants and Literals in C

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In C, constants and literals are fundamental concepts used to represent fixed values in a program.

Constants

Constants are values that do not change during the execution of a program. They can be of various types, including integer, floating-point, character, and more. In C, constants can be defined using the const keyword or using the #define preprocessor directive.

1. Using const Keyword

You can declare a constant variable using the const keyword. Once a variable is declared as const, its value cannot be modified.

const int maxSize = 100;
const float pi = 3.14159;
const char newline = '\n';

2. Using #define Preprocessor Directive

You can also define constants using the #define directive. This method does not create a variable but replaces the constant’s name with its value during preprocessing.

#define MAX_SIZE 100
#define PI 3.14159
#define NEWLINE '\n'

Literals

Literals are the actual values assigned to constants or variables. They represent fixed values written directly in the code. C supports several types of literals:

1. Integer Literals

Integer literals represent whole numbers without any fractional part.

int a = 10;   // Decimal literal
int b = 0xFF; // Hexadecimal literal (prefix 0x or 0X)
int c = 077;  // Octal literal (prefix 0)

2. Floating-Point Literals

Floating-point literals represent numbers with a fractional part.

float x = 3.14;
double y = 0.12345;

3. Character Literals

Character literals represent single characters enclosed in single quotes.

char ch1 = 'A';
char ch2 = '\n'; // Newline character

4. String Literals

String literals represent a sequence of characters enclosed in double quotes.

char str[] = "Hello, World!";

5. Boolean Literals

In C, there’s no built-in boolean type like in C++, but you can use 0 and 1 to represent false and true, respectively.

int isTrue = 1;  // True
int isFalse = 0; // False

Example Program

Here’s an example that demonstrates the use of constants and literals in C:

#include <stdio.h>

#define PI 3.14159  // Define a constant using #define

int main() {
    const int radius = 5; // Define a constant using const
    float area;

    // Using literals and constants
    area = PI * radius * radius;

    printf("Area of the circle: %.2f\n", area);

    return 0;
}

In this program, PI is defined using #define, and radius is defined using const. The literal 5 is used as the value for radius, and the literal 2 is used in the printf format specifier.

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