Introduction
Checking whether a number is prime is one of the most fundamental tasks in mathematics and programming. A prime number is greater than 1 and divisible only by 1 and itself. In this article, we’ll show you how to create a C program to check whether the given number is prime or not using basic loops and condition checks.
What is a Prime Number?
A prime number has exactly two distinct factors: 1 and itself. Examples of prime numbers include 2, 3, 5, 7, and 11. Numbers like 4, 6, 8, and 9 are not prime since they have more than two factors.
C Program to Check Prime Number
#include <stdio.h>
int main() {
int num, i, isPrime = 1;
printf("Enter a number: ");
scanf("%d", &num);
if (num <= 1) {
isPrime = 0;
} else {
for (i = 2; i <= num / 2; i++) {
if (num % i == 0) {
isPrime = 0;
break;
}
}
}
if (isPrime)
printf("%d is a Prime Number.\n", num);
else
printf("%d is Not a Prime Number.\n", num);
return 0;
}
Explanation of the Code
- Input: Accept a number from the user.
- Check:
- If the number is less than or equal to 1, it’s not prime.
- Loop from 2 to half of the number.
- If the number is divisible by any of these, it is not prime.
- Output: Display the result based on the check.
Sample Output
Enter a number: 17
17 is a Prime Number.
Enter a number: 20
20 is Not a Prime Number.
Use Cases of Prime Number Logic in Programming
- Cryptography
- Data compression
- Algorithmic challenges
- Prime factorization applications
Conclusion
This C program to check prime number is a great example to practice loop and condition-based logic. You can further optimize it by checking up to the square root of the number instead of half, which improves performance in larger inputs.