Recurring error within loop C

Question

I just have a loop that returns to the start if a invalid option has been entered

    do{                     
        printf("Please enter a option, Press 'q' to quit\n"); 
        scanf("%d",&option);

        if(option == 1){
            option1(...);
            break;
        }else if(option == 2){
            option1(...);
            break;
        }else if(option == 3){
            option1(...);
            break;
        }else if(option == false){
            printf("exit\n");
            exit(EXIT_SUCCESS);
        }else{
            continue;
        }
    } while(true);

My problem is

If I run it and enter a input eg: '5' it returns to the start of the do statement and I have to enter another input.

If I enter 'q' to quit the loop goes crazy and keeps repeating itself.

What type is option? And why are you comparing it to false? — David Schwartz
– David Schwartz, Commented Oct 20, 2014 at 10:01
You could read them as characters (char) and compare them to characters '1', '2', 'q'. Beware newline characters. — Gunther Van Butsele
– Gunther Van Butsele, Commented Oct 20, 2014 at 10:06

ani627 · Accepted Answer · 2014-10-20 10:18:20Z

3

If you want to quit the program using q, you should declare variable option as char.

For example:

#include <stdio.h>
#include <stdlib.h>

int main()
{
    char option;
    do
    {                     
        printf("Please enter a option, Press 'q' to quit\n"); 
        scanf(" %c",&option);

        if(option == '1')
        {
            //option1(...);
            printf("%c",option);
            break;
        }
        else if(option == '2')
        {
            //option1(...);
            printf("%c",option);
            break;
        }
        else if(option == '3')
        {
            //option1(...);
            printf("%c",option);
            break;
        }
        else if(option == 'q')
        {
            printf("exit\n");
            exit(EXIT_SUCCESS);
        }
        else
        {
            continue;
        }
    } while(1);
    return 0;
}

edited Oct 20, 2014 at 10:18

answered Oct 20, 2014 at 10:08

ani627

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Comments

Peter - Reinstate Monica · Accepted Answer · 2014-10-20 10:07:24Z

-1

The 'q' is not read with scanf("%d".... option therefore probably has none of the values switched over, so that the default case is executed which repeats the loop. That's what you see. Remedy:

Any non-numeric input means break: Just leave everything as is but change continue to break and exit the loop.
Catch non-numerical input and handle it. The scanf manual page (http://linux.die.net/man/3/scanf) says:

These functions return the number of input items successfully matched and assigned

You could check the scanf return value and, if 0, try to scanf the letter in another statement; if 'q', break.
Read a char right away (seems cleanest) and switch over the char, not the int value represented by it.

edited Oct 20, 2014 at 10:07

answered Oct 20, 2014 at 10:00

Peter - Reinstate Monica

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