CODEWITHSUNDEEP
c
north.mister
north.mister

Reputation: 510

Issue using boolean compares in C

I am attempting to check for "y" or "n" and if the input is outside of that continue to ask the user to re-enter their response.

What I currently have:

do{
   printf("Press 'y' to go again or 'n' to quit: ");
   scanf("%s", goAgain);
   result = strncmp(goAgain, yes, 1);
   result2 = strncmp(goAgain, no, 1);
   printf("%d %d\n", result, result2);

}while(result != 0 || result2 != 0);

I know this isn't efficient, I've been trying random things while debugging. In this setup the yes and no are both char * variables. yes contains "y" and no contains "n"

The output of the last printf gave me 0 for result and 11 for result2. This should have dropped out of the do while since I used an OR. Am I doing something obviously stupid or is there some quirk of C that I ma missing (also...this is the first C program I have written so please explain a bit on any C specific suggestions)

Thanks

Edit: Thanks for the replies....that was a rather stupid mistake I should have caught. Now, is there a better way of doing this? The way I have currently feels really clunky, and I don't see any way to make it all that much less clunky (other than directly moving the strncmp's into the while statement)

Upvotes: 1

Views: 88

Answers (3)

BLUEPIXY
BLUEPIXY

Reputation: 40155

char goAgain;
while(1){
    printf("hello\n");
    do{
        printf("\nPress 'y' to go again or 'n' to quit: ");
    }while(scanf(" %c", &goAgain) == 1 && goAgain != 'y' && goAgain != 'n');

    if(goAgain == 'n')//there is no need to check for 'y'
        break;
}

Upvotes: 0

Bogy
Bogy

Reputation: 964

strncmp(str1,str2,num) function returns an integral value indicating the relationship between the strings:

  • A zero value indicates that the characters compared in both strings form the same string.
  • A value greater than zero indicates that the first character that does not match has a greater value in str1 than in str2; And a value less than zero indicates the opposite.

Upvotes: 1

Greg Hewgill
Greg Hewgill

Reputation: 994937

If result is 0 and result2 is 11, then 

result != 0 || result2 != 0
0 != 0 || 11 != 0
false || true
true

which means the while loop will continue looping.

Upvotes: 2

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