Thread: help with this tutorial program: invalid operands to binary( - )

Hello, I am just going over tutorial on line and working on this character handling program from on line tutorial.

First of all, I just copy the program but it doesn't compile.
It complains that (int)cp-in_line is illegal

cha_handle.c:21: error: invalid operands to binary - (have âintâ and âchar *â)


Also, I don't understand why in_line(begining of array) need to be subtracted from current position in array(denoted by cp)...

Any help would be appreciated.

thank you.

Code:

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

#define LINELNG 100 /* max length of input line */

main() {
   char in_line[LINELNG];
   char *cp;
   int c;

   cp = in_line;
   while (  ( c=getc(stdin) ) != EOF   ) {
       if (  cp == &in_line[LINELNG-1] || c == '\n' ) {
            *cp = 0;
            if ( strcmp( in_line, "stop" ) == 0 )
                  exit( EXIT_SUCCESS );
            else
                  /* printf("line was %d characters long\n", (int)cp-in_line); */
                  printf("line was %d characters long\n",
                        (int)cp-in_line);
            cp = in_line;
       }
       else
           *cp++ = c;
    }
    exit(EXIT_SUCCESS);
}