strchr 字符c在字符串中出现的位置 实现

;***
;char *strchr(string, chr) - search a string for a character
;
;Purpose:
;       Searches a string for a given character, which may be the
;       null character '\0'.
;
;       Algorithm:
;       char *
;       strchr (string, chr)
;       char *string, chr;
;       {
;         while (*string && *string != chr)
;             string++;
;         if (*string == chr)
;             return(string);
;         return((char *)0);
;       }
;
;Entry:
;       char *string - string to search in
;       char chr     - character to search for
;
;Exit:
;       returns pointer to the first occurence of c in string
;       returns NULL if chr does not occur in string
;
;Uses:
;
;Exceptions:
;
;*******************************************************************************