Code for string library functions

                   String Copy

char *strcpy( char            *s1, const char   *s2)

{

      char        *s = s1;

      while ((*s1++ = *s2++));

      return s;

}

String Length

int strlen(const char *s)

{

      int   l = 0;

      while (*s++) l++;

      return l;

}

String concat

char *strcat(char *s1, char *s2)

{

      char  *s = s1;

      while (*s1) s1++;

      while (*s2 ) {

            *s1++ = *s2++;

            n--;

      }

      *s1='\0';

      return s;

}

String compare

int strcmp(const char   *s1,const char    *s2)

{

      while ((*s1 || *s2) && n--)

            if (*s1++ != *s2++)

                  return (*--s1 - *--s2);

      return 0;

}

To lower

char tolower(char c)

{

      if (isupper(c))

        return c + ('a' - 'A');

        else

        return c;

}

To upper

char toupper(char c)

{

  if (islower(c))

      return c - ('a' - 'A');

  else

      return c;

}