Answer to Question #313937 in C for Laurente

Question

Write a menu driven program which has the following options:

1. Factorial of a number

2. Prime or not

3. Odd or Even

4. Exit

Once a menu item is selected the appropriate action should be taken and once 

this action is finished, the menu should reappear. Unless the user selects the “Exit” 

option the program should continue to work.

Answer 1

#include <stdio.h>
#include <stdbool.h>


long factorial(int n) {
    long res = 1;
    int i;


    for (i=2; i<=n; i++) {
        res *= i;
    }
    return res;
}


bool is_prime(int n) {
    int i;


    if (n < 2) {
        return false;
    }
    if (n == 2) {
        return true;
    }
    if (n%2 == 0) {
        return false;
    }


    i = 3;
    while (i*i <= n) {
        if (n % i == 0) {
            return false;
        }
        i += 2;
    }
    return true;
}


bool is_even(int n) {
    return n%2 == 0;
}


int main() {
    int ans=0, n;
    long f;


    while (ans != 4) {
        printf("1. Factorial of a number\n");
        printf("2. Prime or not\n");
        printf("3. Odd or Even\n");
        printf("4. Exit\n");
        printf("> ");
        scanf("%d", &ans);


        switch (ans) {
        case 1:
            printf("Enter an integer: ");
            scanf("%d", &n);
            f = factorial(n);
            printf("The factorial is %ld\n", f);
            break;


        case 2:
            printf("Enter an integer: ");
            scanf("%d", &n);
            if ( is_prime(n) ) {
                printf("The number is prime\n");
            }
            else {
                printf("The number is not prime\n");
            }
            break;
        case 3:
            printf("Enter an integer: ");
            scanf("%d", &n);
            if ( is_even(n) ) {
                printf("The number is even\n");
            }
            else {
                printf("The number is odd\n");
            }
            break;
        }
        printf("\n");
    }
    return;
}