Ruby conditional

Ruby provides several common conditional constructs. Here we will explain all conditional statements and modifiers Ruby available.

Rubyif ... else statement

grammar

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

ifexpression for conditional execution. Valuefalseandnilas false, other values are true. Please note, Ruby use elsif, instead of using else if and elif.

If theconditionalis true, then thecode.If theconditionalis not true, else clause specified in thecodeis executed.

We usually omit the reserved word then. If you want to write complete if the formula in a row, then you must be separated by type and conditions of the program blocks. As follows:

if a == 4 then a = 7 end

Examples

#!/usr/bin/ruby
# -*- coding: UTF-8 -*-

x=1
if x > 2
   puts "x 大于 2"
elsif x <= 2 and x!=0
   puts "x 是 1"
else
   puts "无法得知 x 的值"
end

try it"

Examples of the above output:

x 是 1

Rubyif modifiers

grammar

code if condition

if the phrase means that when modified only if the conditions on the right of establishment if the left expression execution. That is, ifconditionalis true, then thecode.

Examples

#!/usr/bin/ruby

$debug=1
print "debug\n" if $debug

try it"

Examples of the above output:

debug

Rubyunless the statement

grammar

unless conditional [then]
   code
[else
   code ]
end

unless the contrary-acting formula and if, that is, if theconditionalis false, then executecode.If theconditionalis true, else clause specified in thecodeis executed.

Examples

#!/usr/bin/ruby
# -*- coding: UTF-8 -*-

x=1
unless x>2
   puts "x 小于 2"
 else
  puts "x 大于 2"
end

try it"

The above example output is:

x 小于 2

Rubyunless modifiers

grammar

code unless conditional

If theconditionalis false, executecode.

Examples

#!/usr/bin/ruby
# -*- coding: UTF-8 -*-

$var =  1
print "1 -- 这一行输出\n" if $var
print "2 -- 这一行不输出\n" unless $var

$var = false
print "3 -- 这一行输出\n" unless $var

try it"

Examples of the above output:

1 -- 这一行输出
3 -- 这一行输出

Rubycase statement

grammar

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

caseexpressionof a judge first match, then branch on the match result.

It uses the=== operator to compare whenthe specifiedexpression,if consistent, then the implementation of the contentwhensection.

We usually omit the reserved word then. If you want to write complete when formula in a row, then you must be separated by type and conditions of the program blocks. As follows:

when a == 4 then a = 7 end

therefore:

case expr0
when expr1, expr2
   stmt1
when expr3, expr4
   stmt2
else
   stmt3
end

Substantially similar:

_tmp = expr0
if expr1 === _tmp || expr2 === _tmp
   stmt1
elsif expr3 === _tmp || expr4 === _tmp
   stmt2
else
   stmt3
end

Examples

#!/usr/bin/ruby
# -*- coding: UTF-8 -*-

$age =  5
case $age
when 0 .. 2
    puts "婴儿"
when 3 .. 6
    puts "小孩"
when 7 .. 12
    puts "child"
when 13 .. 18
    puts "少年"
else
    puts "其他年龄段的"
end

try it"

The above example output is:

小孩

When "expression" part of the case is omitted, the calculation condition when a part of true expression.

foo = false
bar = true
quu = false

case
when foo then puts 'foo is true'
when bar then puts 'bar is true'
when quu then puts 'quu is true'
end
# 显示 "bar is true"