/* str_cmp : Comapares the character strings s1 and s2, and
returns negative, zero or positive if s1 is
lexicographically less than, equal to, or greater than s2.
The value is obtained by subtracting the characters at the
first position where s1 and s2 disagree */

/* return < 0 if s1<s2, 0 if s1==s2, >0 if s1>s2 */
int str_cmp (char *s1, char *s2)
{
    while(*s1++ == *s2++) {
          if (*s1 == '\0')
              return 0;
    }
    return *S1 - *s2;
}

#include<stdio.h>
#include<conio.h>
int xstrcmp(char*,char*);
void main()
{
int c;
char a1[20],a2[20];
printf("enter the two strings :");
gets(a1);
gets(a2);
c=xstrcmp(&a1[0],&a2[0]);
printf("%d",c);
getch();
}
int xstrcmp(char *a,char *a1)
{
  if((*a)!=(*a1))
return((*a)-(*a1));
else if((*a)!='\0' &&  (*a1)!='\0')
{
(*a)++;
(*a1)++;
xstrcmp(a,a1);
}
else
return 0;
}

sorry ... i made a small logical problem in a above posted
answer ... so this program will work out correctly.....

#include<stdio.h>
#include<conio.h>
int xstrcmp(char*,char*);
void main()
{
int c;
char a1[20],a2[20];
printf("enter the two strings :");
gets(a1);
gets(a2);
c=xstrcmp(&a1[0],&a2[0]);
printf("%d",c);
getch();
}
int xstrcmp(char *a,char *a1)
{
  if((*a)!=(*a1))
return((*a)-(*a1));
else if((*a)!='\0' || (*a1)!='\0')
{
(a)++;
(a1)++;
xstrcmp(a,a1);
}
else
return 0;
}