How to Negate a Number in Ruby?

Converting positive number to negative and vice versa in Ruby

In Ruby, you can negate a number (i.e. convert a positive number to negative, and a negative to positive) in the following ways:

Using Unary Minus Operator

You may negate a number using the unary minus operator (-) like so:

-n

This would convert a positive number to a negative number, and a negative number to a positive number. For example, you can use this in the following way:

def negate(num)
    -num
end

puts negate(1234) #=> -1234
puts negate(-1234) #=> 1234

0 is a special case, which would always return 0 when negated:

# ...
puts negate(0) #=> 0
puts negate(-0) #=> 0

Using Arithmetic Operators

You may convert a positive number to negative or vice versa by simply multiplying it by -1:

n * -1

Similarly, you may divide the number by -1 to achieve the same:

n / -1

Alternatively, you may subtract the number from 0:

0 - n

You could use any of these to convert a positive number to a negative number and vice versa, for example, like so:

def negate(num)
    num * -1
end

puts negate(1234) #=> -1234
puts negate(-1234) #=> 1234
def negate(num)
    num / -1
end

puts negate(1234) #=> -1234
puts negate(-1234) #=> 1234
def negate(num)
    0 - num
end

puts negate(1234) #=> -1234
puts negate(-1234) #=> 1234

In any case, 0 would always return 0 when negated:

# ...
puts negate(0) #=> 0
puts negate(-0) #=> 0

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