C Program, Switch menu endless loop

Question

Okay It now loops correctly but when you give it an input e.g. '2' it just goes to the default case.

 print_Menu() {
        while ( 1 )
    {
        printf("=============================================\n");
        printf("MENU\n");
        printf("=============================================\n");
        printf("1. Do stuff\n2. Do more stuff\n3. Do even more stuff\n4. Quit\n");
        printf("Choose an option: ");

        scanf(" %s*", &selection);


        switch (selection) {
            case 1:
                /*do your thing for option 1*/
                printf("thing 1\n");
                break;
            case 2:
                /*do your thing for option 2*/
                printf("thing 2\n");
                break;
            case 3:
                /*do your thing for option 3*/
                printf("thing 3\n");
                break;
            case 4:
                /*do your thing for option 3*/
                printf("quiting app\n");
                exit(0);
                break;
            default:
                printf(" Invalid selection\n");
               // print_Menu();
                break;
        }
      }

By incorrect input you mean an integer that is not in the range 1-4, or do you mean something that is not an integer? — Filipe Gonçalves
– Filipe Gonçalves, Commented Nov 15, 2014 at 13:39
Do you really want to call the function recursively on the default case? — Leeor
– Leeor, Commented Nov 15, 2014 at 13:39

Spikatrix · Accepted Answer · 2014-11-15 13:44:35Z

3

Just add

scanf("%*s");

in the default case to clear the invalid character(s) from the input buffer.The * tells scanf to scan a string and then discard it.

scanf fails to get an integer and returns 0 when you enter any other thing other than an integer. This data does not get consumed by the scanf and hence, remains in the stdin.When scanf is called for the second time,it sees the character which you typed in earlier and then again fails to read an integer.This will then result in an infinite loop

edited Nov 15, 2014 at 13:44

answered Nov 15, 2014 at 13:38

Spikatrix

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8 Comments

Filipe Gonçalves Over a year ago

@Sparky3295 And don't call printMenu() recursively.

Spikatrix Over a year ago

@Sparky3295 ,Also specify the return type before the function definition.(I think you need void there)

Sparky3295 Over a year ago

Okay that worked, but now when I enter an option it just goes straight to the default.

Spikatrix Over a year ago

@Sparky3295 , What did you enter?

Sparky3295 Over a year ago

when I entered an option e.g 1, it would just call the default case and not case 1. I've used a while loop now so that I don't recursively call print_Menu() and that seems to do what I want it to.

|

BLUEPIXY · Accepted Answer · 2014-11-15 13:42:43Z

0

if(1!=scanf("%d", &selection)){
    while(getchar() != '\n');
    selection = -1;
}

answered Nov 15, 2014 at 13:42

BLUEPIXY

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