How to use the scanf( ) int C ?

naihe2010 · 11-29-2005, 05:11 PM

When I want to input a char, is scanf("%c", &ch) right?

I used it, but it doesn't work well.

So I tried it eight times,like :

Code:

scanf("%c", &ch);
scanf("%c", &ch);
scanf("%c", &ch);
scanf("%c", &ch);
scanf("%c", &ch);
scanf("%c", &ch);
scanf("%c", &ch);
scanf("%c", &ch);

and the 2ed, 4th, 6th, 8th line worked. That is, I can only input 4 chars.

Why?

vivekr · 11-29-2005, 06:30 PM

Try using getchar().
Actually the i/p should fail during 2,4,... since \n supplied after entering the required character will remain in the buffer and will be accepted as the next character.
Anyway, u also try fflush(stdin) before scanf statements.

BrianK · 11-29-2005, 06:31 PM

how are you testing it? scanf reads the enter key as an input, so if you test by running & then typing a character, followed by an enter key, you're actually giving it two inputs. try this:

Code:

  scanf("%c", &ch);
  printf("%c\n",ch);
  scanf("%c", &ch);
  printf("%c\n",ch);
  scanf("%c", &ch);
  printf("%c\n",ch);
  scanf("%c", &ch);
  printf("%c\n",ch);
  scanf("%c", &ch);
  printf("%c\n",ch);
  scanf("%c", &ch);
  printf("%c\n",ch);
  scanf("%c", &ch);
  printf("%c\n",ch);
  scanf("%c", &ch);
  printf("%c\n",ch);

run it, then type give it the input "1234567890"<enter> - it will give you back 1 through 8. If you give it:
1<enter>
2<enter>
...

it will give you back a 1, then a newline, then a 2 then a newline, etc. through 4

naihe2010 · 11-29-2005, 08:36 PM

But how can I get 1 char every time ?

Wim Sturkenboom · 11-29-2005, 10:51 PM

Place the terminal in raw mode. Have a look at man cfmakeraw.

spaaarky21 · 11-30-2005, 12:43 AM

Quote:

Originally posted by naihe2010
But how can I get 1 char every time ?

Well, the code you posted seems a little "generic" so it's hard to tell what you are trying to accomplish but to read a char 8 times, why not try something like this:

Code:

for(int i=0; i<8; i++)
{
    scanf("%c", &ch);
    while(ch=='\n')  // If the char was a linebreak, keep scanning until you get one that isn't
        scanf("%c", &ch);

    // Do something with the char here
}

I'm not really sure what you are after but hopefully this might help. If you only want to read numbers of letters, ctype.h contains a function isalnum() that will tell you if a character is either a number of letter. You could use that in the while loop above to skip everything else, including white space.

HTH
Brandon

naihe2010 · 11-30-2005, 12:59 AM

In my whole program, I wrote lots of scanf().
But some scanf() doesn't work well. That is, they get the '\n' from the last scanf() .
It 's so disgusting.
I want only get a char, but doesn't influence the next scanf() to get a char narmally.

Wim Sturkenboom · 11-30-2005, 02:35 AM

Quote:

Originally posted by naihe2010
It 's so disgusting.

Write your own scanf routine if you don't like it. I don't use scanf functions for user input because of this 'unpredictable' behaviour. I always use fgets(buffer,size,stdin) and do the conversions myself. That way, the behaviour is always predictable (the newline is included in the buffer).

PS when you analyse the behaviour, it's probably not as unpredictable as it looks.