question: private long checkZone ( String MGRSString ) { int i = 0 ; int j = 0 ; int num_digits = 0 ; long error_code = MGRS_NO_ERROR ; while ( i < MGRSString . length ( ) && MGRSString . charAt ( i ) == ' ' ) { i ++ ; } j = i ; while ( i < MGRSString . length ( ) && Character . isDigit ( MGRSString . charAt ( i ) ) ) { i ++ ; } num_digits = i - j ; if ( num_digits > 2 ) error_code |= MGRS_STRING_ERROR ; else if ( num_digits <= 0 ) error_code |= MGRS_NOZONE_WARNING ; return error_code ; }
target:  The function Check_Zone receives an MGRS coordinate string. If a zone is given, MGRS_NO_ERROR is returned. Otherwise, MGRS_NOZONE_WARNING. is returned.