Ruby | unless Statement and unless Modifier

Ruby provides a special statement which is referred as unless statement. This statement is executed when the given condition is false. It is opposite of if statement. In if statement, the block executes once the given condition is true, however in unless statement, the block of code executes once the given condition is false. Unless statement is used when we require to print false condition, we cannot use if statement and or operator to print false statements because if statement and or operator always works on true condition. Syntax:

unless condition

   # code

else

  # code

end

Here else block is executed when the given condition is true. Flow Chart: Example: Ruby

# Ruby program to illustrate unless statement 

# variable a
a = 1

# using unless statement
# here 1 is less than 4
unless a > 4
    
    # this will print as
    # condition is false
    puts "Welcome!"

else
    puts "Hello!"
    
end

Output:

Welcome!

unless Modifier: You can also use unless as a modifier to modify an expression. When you use unless as a modifier the left-hand side behaves as a then condition and right-hand side behaves as a test condition. Syntax:

statement unless condition

Example: Ruby

# Ruby program to illustrate 
# unless modifier 

# variable b
b = 0

# unless is behave as a modifier
# here 'b += 2 ' is the statement
# b.zero? is the condition
b += 2 unless b.zero?
    puts(b)

Output:

0