Conditional statements in Ruby language

Conditional statement is used to perform decision making operations based on some condition. Decision making process in programming is similar to decision making in real life. For example, a certain block of code needs to be executed when some condition is fulfilled.

A programming language uses conditional statements to control the flow of execution of the program based on certain conditions.

There are various types of conditional statements in Ruby.

• if, elsif, else Statement
• ?: ternary operator
• unless statement
• case statement

Ruby if, elsif, else statement

This is the basic type of conditional statement. It executes a code block if condition is true. If condition is false, code block of else clause is executed.

Syntax

if condition [then]
   code...
elsif condition [then]
   code...
else
   code...
end

The elsif, then and else part are optionals and required on usage basis.

Example

num = 10

if num.even?
  puts "Number is even"
elsif num.odd?
  puts "Number is odd"
else
  puts "Invalid number"
end

if modifier

Executes code if condition is true. This can be used when else part is unnecessary.

num = 10
puts "Number is even" if num.even?

Ruby Ternary Operator ( ?: )

The ternary operator results to only one value based on some condition. It is used in place of the if-else statement.

Syntax

condition ? return this value if true : return this value if false

Example

5 < 10 ? puts("5 is less than 10") : puts("5 is greater than 10")

# output
5 is less than 10

unless statement

It is similar to if-else statement however it executes the code block when condition is false. If the condition is true, code block in the else clause is executed.

Syntax

unless condition [then]
  code
else
  code
end

The else part is optional and required on usage basis.

Example

count = 1
unless count >= 5
  puts "count is less than 5"
else
  puts "count is greater than 5"
end

# output
count is less than 5

unless modifier

Executes code if condition is false. This can be used when else part is unnecessary.

stop = false
puts "Continue coding ..." unless stop

Ruby case statement

Ruby case statement is similar to switch statement in other languages.

Syntax

case expression
when expression [, expression ...] [then]
  code
else
  code
end

It compares the expression specified by case with the condition of when clause(s) and execute the code block of matching when clause.

If no when clauses match, case executes the code of the else clause.

Example

num = 5
case
when num < 5 then puts "Number is less than 5"
when num == 5 then puts "Number equals to 5"
when num > 5 then puts "Number is greater than 5"
else puts "Invalid number"
end

# output
Number equals to 5

Ruby case is basically similar to if-elsif-else statement.

Above example can be translated as

num = 5
if num < 5
  puts "Number is less than 5"
elsif num == 5
  puts "Number equals to 5"
elsif num > 5
  puts "Number is greater than 5"
else
  puts "Invalid number"
end