char *strlower(string)
    /* Transforms all characters in string to lower case */
    char *string;  /* String to transform */
        {
        char *pc;

        /* Save the starting address */
        pc = string;

        while (*string)
            {
            if (isupper(*string))
                *string = tolower(*string);
            string++;
            }

        return pc;
        }
    
    Why not just:

        while (*string)
            {
            *string = tolower(*string);
            string++;
            }

    Personally I prefer: 

        for (; *string; string++)
            *string = tolower(*string);