To make a number a negative number, you simply add the - sign to the left of it. For example, -4 equals, well, negative 4. If we want to make a negative number a positive number, we can say -(-5). This is because two negatives make a positive. Here is how negative and positive numbers work in Perl:

#!/usr/bin/perl

$a = "\n";

print -(-5);

print $a;

print -4 - -2;

print $a;

print -4 - -4;

print $a;

print -4 + 5;

print $a;

print 5 - -6;

print $a;

print +(+5);

print $a;

print 5 - 6;

print $a;

print -5 * 5;

print $a;

print 5 / -5;

The results:

  5

  -2

  0

  1

  11

  5

  -1

  -25

  -1

Your Assignment: Math

In addition to assigning a value to a variable, you can also perform math at the same time. For instance, let's say that we have a variable and we want to increase its value by ten. Here is one way of doing it:

#!/usr/bin/perl

$value = 10;

print $value . "\n";

$value = $value * 10;

print $value;

This assigns the value 10 to the variable $value, prints it,  and then takes the amount in the variable and multiplies it by ten, reassigns it, and prints it once more. Resulting in:

  10

  100

An easier way to do this is with the *= operator:

#!/usr/bin/perl

$value = 10;

print $value . "\n";

$value *= 10;

print $value;

Giving us the same result:

  10

  100

It may not seem like a huge time saver, but over time it can be.

You can do this with the other math operators as well, like so:

#!/usr/bin/perl

$value = 10;

print $value . "\n";

$value *= 10;

print $value . "\n";

$value +=2;

print $value . "\n";

$value -= 1;

print $value . "\n";

$value /= 2;

print $value . "\n";

$value **= 2;

print $value . "\n";

The result is:

  10

  100

  102

  101

  50.5

  2550.25