Introduction to Ruby

If-Else-Elsif Statements

This is what if-else-elsif statements look like in Ruby. Elsif means "Else If"

if [condition_1]
   do_something
elsif [condition_2]
   do_something_else
else
   do some_default_action
end

Example : Given Three positive numbers, a, b, c; are they sides of an isoceles, equilateral or scalene triangle ? Or do they not form a triangle at all ?

def kindOfTriangle(a,b,c)

if (a == b) && ( b == c ) && ( a == c)

return "equilateral"

elsif ( a + b < c ) || ( a + c < b ) || ( b + c < a )

return "not a triangle"

elsif (a == b ) || ( b == c ) || ( c == a)

return "isoceles"

else

return "scalene"

end

puts kindOfTriangle(5,5,5)

puts kindOfTriangle(10,10,7)

puts kindOfTriangle(30,10,10)

puts kindOfTriangle(3,4,5)

The Output is :

equilateral

isoceles

not a triangle

scalene

If you want to run it quickly, you could try it out in the Interactive Ruby Shell (irb) :

irb(main):017:0> def kindOfTriangle(a,b,c)
irb(main):018:1> if (a == b) && ( b == c ) && ( a == c)
irb(main):019:2> return "equilateral"
irb(main):020:2> elsif ( a + b < c ) || ( a + c < b ) || ( b + c < a )
irb(main):021:2> return "not a triangle"
irb(main):022:2> elsif (a == b ) || ( b == c ) || ( c == a)
irb(main):023:2> return "isoceles"
irb(main):024:2> else
irb(main):025:2* return "scalene"
irb(main):026:2> end
irb(main):027:1> end
=> nil
irb(main):028:0>
irb(main):029:0* puts kindOfTriangle(5,5,5)
equilateral
=> nil
irb(main):030:0> puts kindOfTriangle(10,10,7)
isoceles
=> nil
irb(main):031:0> puts kindOfTriangle(30,10,10)
not a triangle
=> nil
irb(main):032:0> puts kindOfTriangle(3,4,5)
scalene
=> nil
irb(main):033:0>

If Statements

code if condition

def demonstrateIf(x)

puts x

puts (x+1) if x == 5

puts (x+2) if x == 6

end

demonstrateIf(4)

demonstrateIf(5)

demonstrateIf(6)

Output:

5 /// 5

6 /// 5 + 1

6 /// 6

8 /// 6 + 2

**Ruby Unless Statement**

"Unless" runs a code fragment if the conditional is false.

unless [conditional]

[code_fragment]

else

[code_fragment]

end

x = 10

unless x < 10

puts "Unless1"

else unless x < 5

puts "Unless2"

else

puts "Out of all unless statements"

end

Output:

Unless1

irb(main):001:0> x = 10
=> 10
irb(main):002:0> unless x < 10
irb(main):003:1> puts "Unless1"
irb(main):004:1> else unless x < 5
irb(main):005:2> puts "Unless2"
irb(main):006:2> else puts "Out of all Unless Statements"
irb(main):007:2> end
irb(main):008:1> end
Unless1
=> nil

**Demonstrating the Ruby Case Statement**

Using case with numeric data :

def testCase(x) # x is a positive integer

case x

when 0..9

puts "Single Digit"

when 10..99

puts "Double Digit"

when 100..999

puts "Triple Digit"

else

puts "More than three digits" # By default, this will be printed

end

testCase(1)

testCase(2)

testCase(30)

testCase(100)

testCase(1000)

Output:

Single Digit

Double Digit

Triple Digit

More than three digits

Using Case with Strings :

def testCaseWithString(str)

case str

when "line"

puts "Two Points"

when "triangle"

puts "Three Points"

when "quadrilateral"

puts "Four Points"

else

puts "More than four points, or a shape which we can't figure out"

end

testCaseWithString("triangle")

testCaseWithString("quadrilateral")

testCaseWithString("XYZ")

Output:

Three Points

Four Points

More than four points, or a shape which we can't figure out

Check out some of our other Ruby Tutorials :

Introduction to Ruby and some playing around with the Interactive Ruby Shell (irb) Introduction to Ruby - Conditional statements and Modifiers: If-then, Unless, Case Introduction to Ruby Comments - Single and Multi-Line comments Introduction to Ruby Loops - Using While, Until, For, Break, Next , Redo, Retry
Introduction to Ruby - Arrays - Sorting, Filtering (Select), Transforming, Multi-Dimensional Arrays Introduction to Ruby - Strings Introduction to Ruby - Making a Script Executable Introduction to Ruby - Regular Expressions, Match, Scan
Introduction to Ruby - Computing Factorials Recursively : An Example of Recursion Introduction to Ruby - Binomial Coefficients (nCr) : An Example of Recursion Introduction to Ruby - Computing a Power Set : An Example of Recursion Introduction to Ruby - Towers of Hanoi : An Example of Recursion
Introduction to Ruby - Strings: Substitution, Encoding, Built-In Methods

Basic Data Structures With Ruby

Basic Data Structures in Ruby - Insertion Sort Basic Data Structures in Ruby - Selection Sort Basic Data Structures in Ruby - Merge Sort Basic Data Structures in Ruby - Quick Sort Functional Programming with Ruby
Basic Data Structures in Ruby - Stack Basic Data Structures in Ruby - The Queue Basic Data Structures in Ruby - Linked List - ( A Simple, Singly Linked List) Basic Data Structures in Ruby - Binary Search Tree