Ruby if...else, case, unless
Ruby offers contional structures that are pretty common to modern languages. Here we will explain all the conditional statements and modifiers available in Ruby
Ruby if...else Statement:
Syntax:
if conditional [then]
code...
[elsif conditional [then]
code...]...
[else
code...]
end
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if expressions are used for conditional execution. The values false and nil are false, and everything else are true. Notice Ruby uses elsif, not else if nor elif.
Executes code if the conditional is true. If the conditional is not true, code specified in the else clause is executed.
An if expression's conditional is separated from code by the reserved word then, a newline, or a semicolon.
Example:
#!/usr/bin/ruby
x=1
if x > 2
puts "x is greater than 2"
elsif x <= 2 and x!=0
puts "x is 1"
else
puts "I can't guess the number"
end
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This will produce following result:
Ruby if modifier:
Syntax:
Executes code if the conditional is true.
Example:
#!/usr/bin/ruby
$debug=1
print "debug\n" if $debug
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This will produce following result:
Ruby unless Statement:
Syntax:
unless conditional [then]
code
[else
code ]
end
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Executes code if conditional is false. If the conditional is true, code specified in the else clause
is executed.
Example:
#!/usr/bin/ruby
x=1
unless x>2
puts "x is less than 2"
else
puts "x is greater than 2"
end
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This will produce following result:
Ruby unless modifier:
Syntax:
Executes code if conditional is false.
Example:
#!/usr/bin/ruby
$var = 1
print "1 -- Value is set\n" if $var
print "2 -- Value is set\n" unless $var
$var = false
print "3 -- Value is set\n" unless $var
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This will produce following result:
1 -- Value is set
3 -- Value is set
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Ruby case Statement
Syntax:
case expression
[when expression [, expression ...] [then]
code ]...
[else
code ]
end
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Compares the expression specified by case and that specified by when using the === operator and executes
the code of the when clause that matches.
The expression specified by the when clause is evaluated as the left operand. If no when clauses match, case executes the code of the else clause.
A when statement's expression is separated from code by the reserved word then, a newline, or a semicolon.
Thus:
case expr0
when expr1, expr2
stmt1
when expr3, expr4
stmt2
else
stmt3
end
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is basically similar to the following:
_tmp = expr0
if expr1 === _tmp || expr2 === _tmp
stmt1
elsif expr3 === _tmp || expr4 === _tmp
stmt2
else
stmt3
end
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Example:
#!/usr/bin/ruby
$age = 5
case $age
when 0 .. 2
puts "baby"
when 3 .. 6
puts "little child"
when 7 .. 12
puts "child"
when 13 .. 18
puts "youth"
else
puts "adult"
end
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This will produce following result:
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