я хочу получить входные данные формы в качестве переменной

Да, он сравнивает значение ascii и, если он равен, повторите сравнение в следующем символе.

/* Copyright (C) 1991, 1996, 1997, 2003 Free Software Foundation, Inc. 
   This file is part of the GNU C Library. 

   The GNU C Library is free software; you can redistribute it and/or 
   modify it under the terms of the GNU Lesser General Public 
   License as published by the Free Software Foundation; either 
   version 2.1 of the License, or (at your option) any later version. 

   The GNU C Library is distributed in the hope that it will be useful, 
   but WITHOUT ANY WARRANTY; without even the implied warranty of 
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU 
   Lesser General Public License for more details. 

   You should have received a copy of the GNU Lesser General Public 
   License along with the GNU C Library; if not, write to the Free 
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 
   02111-1307 USA.  */ 

#include <string.h> 
#include <memcopy.h> 

#undef strcmp 

/* Compare S1 and S2, returning less than, equal to or 
   greater than zero if S1 is lexicographically less than, 
   equal to or greater than S2.  */ 
int 
strcmp (p1, p2) 
     const char *p1; 
     const char *p2; 
{ 
  register const unsigned char *s1 = (const unsigned char *) p1; 
  register const unsigned char *s2 = (const unsigned char *) p2; 
  unsigned reg_char c1, c2; 

  do 
    { 
      c1 = (unsigned char) *s1++; 
      c2 = (unsigned char) *s2++; 
      if (c1 == '\0') 
        return c1 - c2; 
    } 
  while (c1 == c2); 

  return c1 - c2; 
}