如果输入了一些无效的输入，如何在切换情况下重复scanf？

Question

I have the following code, where I expect the user to give eiher 's' or 'f' (case insensitive) as input:

/* ... snip ... */
char acc_type;
printf("\n\nENTER HERE\t : ");
scanf("%c",&acc_type);

switch (acc_type)
{
    case 's':
    case 'S':
        printf("\n SAVING ACCOUNT");
        break;

    case 'f':
    case 'F':
        printf("\n FIXED ACCOUNT");
        break;

    default:
    printf("\n INVALID INPUT!!! TRY AGAIN");
}
/* ...  snip ... */

However, the default action doesn't allow me to repeat the whole switch statement. How can I ask for input in his scenario again if the input wasn't valid?

Answer 1

You need a loop, essentially (in pseudo-code):

good_input = 0;

while(good_input == 0) {
    ... prompt for input ...
    if (input == good) {
        good_input = 1;
    }
}

Until something valid is entered, good_input stays 0 and the while() loop continues to prompt for input. Once something good is entered, that flag changes and the code continues on to the next section.

Answer 2

Put the part you want to repeat in a loop, like this:

bool inputOK = false;
do {
    printf("\n\nType S to SAVING ACCOUNT");
    printf("\nType F to FIX ACCOUNT");
    printf("\n\nENTER HERE\t : ");
    scanf("%c",&acc_type);      

    switch (acc_type)
    {
    case 's':
    case 'S':        
        printf("\n SAVING ACCOUNT");
        inputOK = true;
        break;

    case 'f':
    case 'F':        
        printf("\n FIXED ACCOUNT");
        inputOK = true;
        break;

    default:
        printf("\n INVALID INPUT!!! TRY AGAIN");
        break;     // Note: it's wise to use break in EVERY case
    }
} while (inputOK == false);