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This noncompliant code example improperly uses eq to test two numbers for equality. Counterintuitively, this code prints false.

my $num = 02;
# ... 2;
print "Enter a number\n";
my $user_num = <STDIN>;
chomp $user_num;
if ($num eq "02"$user_num) {print "true\n"} else {print "false\n"};

This code will print true if the user enters 2, but false if the user enters 02,The counterintuitive result arises because $num is interpreted as a number. When it is initialized, the 02 string is converted to its numeric representation, which is 2. When it is compared, it is converted back to a string, but this time it has the value 2, so the string comparison fails.

Compliant Solution (Numbers)

This compliant solution uses ==, which interprets its arguments as numbers. This code therefore prints true even though if the right argument to == is explicitly provided as a stringinitialized to some different string like 02.

my $num = 2;
print "Enter a number\n";
my $user_num = 02<STDIN>;
# ...chomp $user_num;
if ($num == "02"$user_num) {print "true\n"} else {print "false\n"};

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The == operator first converts its arguments into numbers by extracting digits from the front of each argument (along with a preceding + or -). Nonnumeric data in an argument is ignored, and the number consists of whatever digits were extracted. A string such as "goodpass" has no leading digits and , so it is thus converted to the numeral 0. Consequently, unless either $password or $correct contains leading digits, they will both be converted to 0 and will be considered equivalent.

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Automated Detection

Bibliography

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