Constants and Variables

In C, constants and variables are used to store data, but they have distinct characteristics and usage. Here’s a brief overview:

Constants in C

1. Definition: A constant is a value that cannot be modified after it is defined.
2. Types of Constants:

• Literal Constants: Directly used values, like numbers and characters

int age = 30; // 30 is a literal constant
char letter = ‘A’; // ‘A’ is a literal constant

• Defined Constants: Created using the #define preprocessor directive

#define PI 3.14

• Const Qualifier: Declares a variable whose value cannot be changed after initialization

const int MAX_USERS = 100;

Variables in C

1. Definition: A variable is a named storage location in memory that can hold different values throughout the program’s execution.
2. Declaration and Initialization:

int userCount; // Declaration
userCount = 0; // Initialization

Usage:

• Variables can be modified at any point in the program.

userCount += 1; // userCount is now 1

Key Differences

• Mutability:
  • Constants cannot be changed once set.
  • Variables can be reassigned throughout the program.
• Usage:
  • Use constants for fixed values (like mathematical constants or configuration).
  • Use variables for data that may change (like counters or user inputs).

Example Code

Here’s a simple example demonstrating both constants and variables:

#include <stdio.h>

#define PI 3.14 // Defined constant

int main() {
const int MAX_USERS = 100; // Const variable
int userCount = 0; // Variable

// Simulating user additions
for (int i = 0; i < 5; i++) {
userCount++; // Increment user count
if (userCount > MAX_USERS) {
printf(“Maximum user limit reached!\n”);
break;
}
}

printf(“Current user count: %d\n”, userCount);
printf(“Value of PI: %f\n”, PI);

return 0;
}

Summary

• Constants: Use #define or const for values that should not change.
• Variables: Use standard data types (like int, float) to store and modify values as needed.