How do I implement isPrime?

Let me try to explain the concept.

A number is called prime if it is only divisible by 1 and itself. If no other number can divide it exactly, then the number is prime.

So to check if a number is prime, we try dividing it by all numbers between 2 and (number - 1).

• If it divides evenly by any of them, it's not a prime number.

• If it doesn’t divide evenly by any, then it's prime.

Here’s a function that checks if a number is prime:

void isPrime(int number) {
    int flag = 0;

    for (int i = 2; i < number; ++i) {
        if (number % i == 0) {
            flag = 1;
        }
    }

    if (flag == 0) {
        printf("%d\n", number);
    }
}

Here,

• We run a loop from 2 to number - 1.

• In each iteration, we check if number is divisible by i.

• If it is divisible, we set flag to 1 (meaning it’s not prime).

• After the loop, if flag is still 0, it means the number is prime, and we print it.

Then, in the main() function, we can call isPrime() for a range of numbers:

int main() {
    
    int x, y;
    scanf("%d %d", &x, &y);
    
    // run the loop from x to y
    // for each iteration of loop call isPrime()
    for (int i = x; i <= y; ++i) {
        isPrime(i);
    }
    
    return 0;
}

Hope this helps and makes the concept clearer! Feel free to reach out if you have more questions or need further assistance.