Write a C Program to Check if a Number is Prime or Not Using For Loop

Write a C Program to Check if a Given Number is Prime or Not Using for Loop

Do you need to check if a given number is a prime number? You can easily do this with the help of the for loop. Here, we'll explain how to write a C program to check if a given number is prime or not using for loop.

What is a Prime Number?

A prime number is a natural number greater than 1 that has no positive divisors other than one and itself. A prime number is an integer greater than 1 that can only be divided evenly by 1 and itself.

Algorithm to Find a Prime Number

1. Start by taking an input number from the user.
2. Run a loop from 2 to the input number - 1 and increment the loop counter by 1 each time.
3. Check if the input number is exactly divisible by the loop counter.
4. If it is divisible, then the number is not a prime number so terminate the loop.
5. Otherwise, check if the loop has reached the last iteration i.e. input_number - 1.
6. If yes, then the number is a prime number so print "Prime" and terminate the loop.

C Program to Check if a Given Number is Prime or Not Using for Loop

#include<stdio.h>

int main() {
    int num, i;
    /* Input a positive integer from user */
    printf("Enter any number: ");
    scanf("%d", &num);

    /* Run a loop from 2 to num - 1 */
    for(i=2; i<num; i++) {

        /* If num is divisible by any number between
         2 and num-1, it is not a prime number */
        if(num % i == 0) {
            printf("%d is not a prime number", num);
            break;
        }
    }

    /* 
     * If num is not divisible by any number between
     * 2 and num-1, it is a prime number
     */
    if(i == num)
        printf("%d is a prime number", num);

    return 0;
}

Enter any number: 10
10 is not a prime number

In the above program, we have used for loop to iterate from 2 to input_number-1. We are checking if the reminder of input_number/loop counter is 0. If it is 0, then the number is not a prime number and we terminate the loop. Otherwise, we check if the loop has reached its last iteration. If yes, then the number is a prime number and we print "Prime".

That's it! The above program checks if a given number is a prime number or not using for loop. Try running the program yourself and see what happens!

Top Resources

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Further Reading:

 For further information and examples, Please visit[ C-Programming From Scratch to Advanced 2023-2024]

Note: If you encounter any issues or specific errors when running this program, please let me know and I'll be happy to help debug them!