Answer to Question #307889 in C for Justin

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. You may use of an infinite while and

switch statement.

Answer 1

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


int menu() {
    char* msg[] = {"Factorial of a number", "Prime or not", 
                   "Odd or Even", "Exit"};
    int i, ans=0;


    for (i=0; i<4; i++) {
        printf("%d. %s\n", i+1, msg[i]);
    }
    printf(">>> ");
    scanf("%d", &ans);


    return ans;
}


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


    for (i=1; i<=n; i++) {
        res *= i;
    }
    return res;
}


bool is_prime(int p) {
    int i;


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


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


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


int main() {
    int ans=0, x;
    long res;


    while (ans != 4) {
        ans = menu();
        switch (ans) {
        case 1:
            printf("Enter an integer: ");
            scanf("%d", &x);
            res = factorial(x);
            printf("Factorial = %ld\n\n", res);
            break;

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

        case 3:
            printf("Enter an integer: ");
            scanf("%d", &x);
            if (is_even(x)) {
                printf("The number is even\n\n");
            }
            else {
                printf("The number is odd\n\n");
            }
            break;

        case 4:
            break;
        
        default:
            printf("Incorrect choice\n\n");
        }
    }

    return 0;
}