#! perl -slw use strict; sub times7 { return $_[ 0 ] * 7; } print "times7( $_ ) returned:", times7( $_ ) for 1, 2, 3, 0, undef, 'fred'; __END__ P:\test>junk times7( 1 ) returned:7 times7( 2 ) returned:14 times7( 3 ) returned:21 times7( 0 ) returned:0 Use of uninitialized value in concatenation (.) or string at P:\test\junk.pl line 8. Use of uninitialized value in multiplication (*) at P:\test\junk.pl line 5. times7( ) returned:0 Argument "fred" isn't numeric in multiplication (*) at P:\test\junk.pl line 5. times7( fred ) returned:0