Functions

#include <stdio.h>

int add(int a, int b) {
    return a + b;
}

int main() {
    int a, b;
    scanf("%d %d", &a, &b);
    printf("Sum = %d\n", add(a, b));
    return 0;
}

#include <stdio.h>

int factorial(int n) {
    if (n <= 1) return 1;
    return n * factorial(n - 1);
}

int main() {
    int n;
    scanf("%d", &n);
    printf("%d! = %d\n", n, factorial(n));
    return 0;
}

#include <stdio.h>

int isPrime(int n) {
    if (n < 2) return 0;
    for (int i = 2; i * i <= n; i++)
        if (n % i == 0) return 0;
    return 1;
}

int main() {
    int n;
    scanf("%d", &n);
    printf(isPrime(n) ? "Prime\n" : "Not Prime\n");
    return 0;
}