详解Ruby之判断语句的条件

=begin
语法：
if 条件1 then
   语句1
elsif 条件2 then
   语句2
elsif 条件3 then
   语句3
else
   语句4
end
=end

 

a = 10
b = 20
if a>b then
   print "a is smaller than b."
elsif a == b then
   print "a equals b."
else
   print "a is larger than b."
end

=begin
语法：
unless 条件 then
   语句
end
=end

 

a = 10
b = 20
unless a>b then
   print "a is smaller than b."
end

# -> "a is smaller than b" will be printed out.

=begin
语法：
case 想要比较的对象
when 值1 then
    语句1
when 值2 then
    语句2
when 值3 then
    语句3
else
    语句4
end
# then是可以省略的
=end

 

array = ["aa", 1, nil]
item = array[0]
   case item
   when String
      puts "item is a String."
   when Numeric
      puts "item is a Numeric."
   else
      puts "item is a something"
   end
#这里比较的是对象的类型，而不是对象的值

p ((1..3) === 2)  #-> true
p /zz/ === "zyzzy"  #-> 2
p String === "xyzzy"  # -> true

 

#在case表达与if语句间转换，用===，符号左边是case的值，右边为case的变量
case A
when value1                   if value1 === A
   语句1                              语句1
when value2                   elsif value2 === A
   语句2                               语句2
else                                else
   语句3                                语句3
end                                 end