Probably simple mistake (newbie)

Hi,

I just started with C like 1 week ago and Ive never coded in my life so bear with me :) as I always try to code stuff from the top of my head that Ive already learned so its really just a very simple code ...

Code:

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#include<stdio.h>

int main(void)
{

  char c;

  //ask user

  while (!(c == 'y' || c == 'Y' || c == 'n' || c == 'N')) {
    printf("Do you agree?: ");
    scanf("%c", &c);

    if (c == 'y' || c == 'Y')
      printf("I agree\n");

    else if(c == 'n' || c == 'N')
        printf("I disagree\n");
  }

}

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The purpose of this code is to ask the user if he "Agrees" and if he types in anything else than "Y/y or N/n" it asks the user again in a loop.

Now the problem is that if you enter any other charakter than "Y/y /N/n" it always prints "Do you agree?: " twice in a row and I cant figure out why.

Thanks in advance.

Welcome to the forum.

First thing, when you paste code, make sure you use "copy as text" from your IDE and/or "paste as text" in your browser.
The colour markup that comes along for the ride from most IDEs is pathetic.

> char c;
Initialise your variables.
If by chance the random initialisation matches your loop exit condition, you're stuck.

> scanf("%c", &c);
%c is rather special in the scanf conversions in that it respects white space (which includes newlines).
So typically you go round your loop twice, once with c='Y' say, and then again with c='\n'.

If you want to avoid this, add a space to the format.

Code:

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scanf(" %c", &c);

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Hi,

thanks for your reply, such a little error but now it works thanks alot. And sorry for including the code wrong I will do better in the future :).

Here's a more concise loop condition

while (strrchr("YN", topper(c)) == NULL)

After topper returns c''s value in uppercase, strrchr looks for the uppercase letter in "YN". If it's not there, strrchr returns NULL.

To use strrchr, you'll need to include ctype.h.

"toupper" (note the "u") is in ctype.h, but strchr is in string.h.

Quote:

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Originally Posted by christop

"toupper" (note the "u") is in ctype.h, but strchr is in string.h.

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Thank you. I should have noticed the typo and corrected it.