Basic operations on strings in C

#include <stdio.h>
#include <conio.h>
#include <string.h>
#include <windows.h>
int xstrlen ( char * ) ;
void xstrcpy ( char *, char * ) ;
void xstrcat ( char *, char * ) ;
int xstrcmp ( char *, char * ) ;
void show ( char * ) ;
int main( )
{
 char s1[ ] = "kicit" ;
 char s2[ ] = "Nagpur" ;
 char s3[20] ;
 int len ;
 system ( "cls" ) ;
 printf ( "String s1: %s\n", s1 ) ;
 len = xstrlen ( s1 ) ;
 printf ( "length of the string s1: %d\n", len ) ;
 printf ( "String s2: %s\n", s2 ) ;
 xstrcpy ( s3, s1 ) ;
 printf ( "String s3 after copying s1 to it: %s\n", s3 ) ;
 xstrcat ( s3, s2 ) ;
 printf ( "String s3 after concatenation: %s\n", s3 ) ;
 if ( xstrcmp ( s1, s2 ) == 0 )
  printf ( "The strings s1 and s2 are similar\n" ) ;
 else
  printf ( "The strings s1 and s2 are not similar\n" ) ;
 return 0 ;
}
/* finds the length of the string */
int xstrlen ( char *s )
{
 int l = 0 ;
 while ( *s )
 {
  l++ ;
  s++ ;
 }
 return l ;
}
/* copies source string s to the target string t */
void xstrcpy ( char *t, char *s )
{
 while ( *s )
 {
  *t = *s ;
  t++ ;
  s++ ;
 }
 *t = '\0' ;
}
/* concatenates the two strings */
void xstrcat ( char *t, char *s )
{
 while ( *t )
  t++ ;
 while ( *s )
  *t++ = *s++ ;
 *t = '\0' ;
}
/* compares two strings s and t for equality */
int xstrcmp ( char *s, char *t )
{
 while ( *s == *t )
 {
  if ( ! ( *s ) )
   return 0 ;
  s++ ;
  t++ ;
 }
 return ( *s - *t ) ;
}