The Ruby **`gcd()` function** returns the GCD of two integers.

> The **GCD** or **Greatest Common Divisor** of two numbers, i.e., `num_1` and `num_2`, is the greatest positive number that divides both the `num_1` and the `num_2`. 

Figure 1, below, shows the visual representation of the `gcd()` function.

# Syntax

```ruby
num_1.gcd(num_2)
# where num_1 and num_2 are the integers whose gcd is to be calculated
```

> If `num_1` or `num_2` or both are *non-integers*, then this function throws an `error`.

# Parameter

This function requires another integer, `(num_2)`, as a parameter.

# Return value

This function returns the GCD of two integers.

# Code

The following example shows how to use the `gcd()` function in Ruby.

#both positive numbers
print "(36).gcd(60) : ",(36).gcd(60) , "\n"

#both negative numbers
print "(-24).gcd(-16) : ",(-24).gcd(-16) , "\n"

#one of the numbers is zero
print "(0).gcd(12) : ",(0).gcd(12), "\n"

#one is negative and another is positive
print "(-9).gcd(18) : ",(-9).gcd(18) , "\n"

What is gcd() in Ruby?

Ruby's gcd() function calculates the greatest positive divisor of two integers, returning an error if non-integers are used.