Thread: scanf issue

Another piece of information for @cooper1200. Keep in mind that reading from stdin (via scanf) isn't the same as reading directly from keyboard (which is more difficult to do). You are reading a "file" through a FILE pointer called stdin. Take a look at the code below:

Code:

#include <stdio.h>

int main( void )
{
  char c;
  int count = 3;

  puts( "Trying to read Y or N 3 times..." );

  while ( count-- )
  {
    // this (or printf, puts, putchar) writes
    // to stdout file stream.
    fputs( "Type Y or N. ", stdout ); 

    // stdout is 'line buffered'. It means that
    // it can retain the chars until a '\n' is found.
    // flushing the buffer garantees all chars will
    // be dumped. The previous fputs didn't write
    // the final \n, hence the flushing.
    fflush( stdout );

    // scanf reads data from stdin file stream.
    // Note the space before %c will ignore all "spaces"
    // as defined by isspace macro on ctype.h
    scanf( " %c", &c );
    switch (c)
    {
      case 'Y':
      case 'y':
        puts( "\nYes!" ); break;
      case 'N':
      case 'n':
        puts( "\nNo!" ); break;
      default:
        printf( "\nFound '\\x%hhx' char. Hey! Y or N, remember?\n", c );
    }
  }
}

Here are three ways to execute this code:

$ ./test
Trying to read Y or N 3 times...
Type Y or N. y

Yes!
Type Y or N. x

Found '\x78' char. Hey! Y or N, remember?
Type Y or N. n

No!

$ echo -e " y x \r\n\t\v\f n" | ./test
Trying to read Y or N 3 times...
Type Y or N.
Yes!
Type Y or N.
Found '\x78' char. Hey! Y or N, remember?
Type Y or N.
No!

$ echo -e " y x \r\n\t\v\f n" > ./input.txt
$ ./test < input.txt
Trying to read Y or N 3 times...
Type Y or N.
Yes!
Type Y or N.
Found '\x78' char. Hey! Y or N, remember?
Type Y or N.
No!

When you don't provide data for stdin (through pipe or redirection), functions as scanf() will wait for data coming from keyboard...
So, thinking abour stdin, stdout and stderr as "files" is useful...

PS: And yes... ignoring "spaces" before is better than after, in this case...

thanks all for your help much appreciated I wound that "scanf(" %c"&yn) worked but will experiment with all the other solutions.
many thanks
coop