Thread: Help with menu and integer selections

I have made a program that offers the user several options from which to choose from. Each one has an integer assigned (e.g. 1,2,3...) and the user enters the number of the option he has selected. I use the scanf function to get the user's choice and the switch statement to branch through the program. Still if I am careless enough to enter a letter instead of a number the program will crash. How can I prevent that?

you can make this in a lot of ways, using a do-while to check whether it's an valid input, but you can use a tricky-way that not always works but sometimes can be very usefull, look at this:

Code:

if (!scanf("%d",&n))
    //invalid input here, error handling
else
    //valid input, the user did enter an integer

But this is a problem when scanf() returns EOF
Also you can do a do-while to check if the input is alphabetic or isdigit, by using the isalpha or isdigit function.

Here's one way to get bulletproof menus with scanf

Code:

#include <stdio.h>

int main(void)
{
    int option;
    
    while (1)
    {
        int rc;
        
        printf("1. Option 1\n2. Option 2\n3. Option 3\n");
        printf("Select an option (ctrl+z to quit): ");
        fflush(stdout);
        
        rc = scanf("%1d", &option);
        if (rc == EOF)
            break;
        
        scanf("%*[^\n]");
        getchar();
        
        if (rc < 1)
        {
            fprintf(stderr, "Bad input, try again...\n");
            continue;
        }
        
        switch (option)
        {
        case 1:
            printf("Option 1\n");
            break;
        case 2:
            printf("Option 2\n");
            break;
        case 3:
            printf("Option 3\n");
            break;
        default:
            fprintf(stderr, "Invalid option\n");
            break;
        }
    }

    return 0;
}