C - Noob error with simple 3-way comparison

Question

Apologies for the dumb question, I'm a bit of a beginner and am having trouble understanding why the following code will not work correctly.

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

int main()
{
    int j = ' ';
    int check = 0;

    printf("\nPlease enter A, B, or C\n");
    j = getch();

    while(check == 0)
    {
        if(j != 'A' || 'B' || 'C')
        {
            printf("\nInvalid entry, please enter either an A, B, or C\n");
            j = getch();
        }
        else
        {
            check = 1;
        }
    }
}

All I want this simple program to do is take in either A, B, or C using getch() (Yes, I need to use getch()) and use my while loop to confirm the entry actually is either an A, a B, or a C. However, I run the program, and even when I enter an A, B, or a C, the program tells me my entry is not valid. Can someone help me here and tell me what I'm doing wrong?

I have a feeling this has to do with the fact that it reads in the character as an ASCII integer, but I'm really not sure how to fix this.

Welcome to Stack Overflow. Please read the [About] page soon. Note that `getch()` is a platform-specific function declared in `` on Windows and in `` on Unix (where its use also requires at least one setup function call). However, the use of `getch()` is actually tangential to your problem. — Jonathan Leffler, Oct 13 '13 at 22:47

score 4 · Answer 1 · answered Oct 13 '13 at 22:27

4

if(j != 'A' || 'B' || 'C')

is equivalent to

if(j != 'A' || 'B' != 0 || 'C' != 0)

Both 'B' and 'C' have non-zero value so the condition will always evaluate true.

I think you want to check that j isn't any of the values listed. If so, the line should be

if(j != 'A' && j != 'B' && j != 'C')

answered Oct 13 '13 at 22:27

simonc

41,632
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Stupid mistake on my part. Thank you very much. – Rob Johnson Oct 13 '13 at 22:35

score 0 · Answer 2 · edited Nov 07 '17 at 00:54

0

Do the following replacements:

int j = ' '; /* to */  char j = ' ';

if(j != 'A' || 'B' || 'C') /* to */ if(j != 'A' && j != 'B' && j != 'C')

j = getch(); /* to */ j=getchar();

Also, for getchar() to work, include <conio.h> if required.

edited Nov 07 '17 at 00:54

Pang

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answered Nov 06 '17 at 18:52

Anmoldeep Singh

41
4

C - Noob error with simple 3-way comparison

2 Answers2