switch statement

switch语句用于运行一组特定的语句，具体取决于表达式的值。 它经常取代一组if…elsif语句，让您对程序有更多的控制和可读性

语法 (Syntax)

简单switch语句的语法如下 -

switch expression do
   case <val> [, <val-1>....] then
      -- Executes when the expression matches one of the values  
   case <val> [, <val-1>....] then
      -- Executes when the expression matches one of the values  
      .....................
   case else
      -- Executes when the expression does not matches any case.  
end if

案例中的必须是原子，文字字符串，常量或枚举。 可以通过用逗号分隔值来指定单个案例的多个值。 默认情况下，当遇到下一个案例时，控制将流向开关块的末尾。

例子 (Example)

#!/home/euphoria-4.0b2/bin/eui
atom marks = 'C'
switch marks do
   case 'A' then
      puts(1, "Excellent!\n" )
   case 'B', 'C' then
      puts(1, "Well done!\n" )
   case 'D' then
      puts(1, "You passed!\n" )
   case 'F' then
      puts(1, "Better try again!\n" )
   case else
      puts(1, "Invalid grade!\n" )
end switch

这会产生以下结果 -

Well done!

switch...with fallthru声明

当switch与给定的表达式值匹配时，将执行switch的case语句，默认情况下它会出现。 默认情况下，当遇到下一个案例时，控制将流向开关块的末尾。

可以更改特定开关块的默认值，以便只要在switch语句中使用with fallthru遇到新案例，控制就会传递给下一个可执行语句 -

语法 (Syntax)

简单switch...with fallthru的语法switch...with fallthru语句如下 -

switch expression with fallthru do
   case <val> [, <val-1>....] then
      -- Executes when the expression matches one of the values  
      break -- optional to come out of the switch from this point.
   case <val> [, <val-1>....] then
      -- Executes when the expression matches one of the values  
      break -- Optional to come out of the switch from this point.
      .....................
   case else
      -- Executes when the expression does not matches any case.  
      break -- Optional to come out of the switch from this point.
end if

例子 (Example)

#!/home/euphoria-4.0b2/bin/eui
atom marks = 'C'
switch marks with fallthru do
   case 'A' then
      puts(1, "Excellent!\n" )
   case 'B', 'C' then
      puts(1, "Well done!\n" )
   case 'D' then
      puts(1, "You passed!\n" )
   case 'F' then
      puts(1, "Better try again!\n" )
   case else
      puts(1, "Invalid grade!\n" )
end switch

这会产生以下结果 -

Well done!
You passed!
Better try again!
Invalid grade!

你可以使用可选的break语句从switch语句中的一个点出来，如下所示 -

#!/home/euphoria-4.0b2/bin/eui
atom marks = 'C'
switch marks with fallthru do
   case 'A' then
      puts(1, "Excellent!\n" )
      break
   case 'B', 'C' then
      puts(1, "Well done!\n" )
      break
   case 'D' then
      puts(1, "You passed!\n" )
      break
   case 'F' then
      puts(1, "Better try again!\n" )
      break
   case else
      puts(1, "Invalid grade!\n" )
      break
end switch

这会产生以下结果 -

Well done!

switch....label声明

switch语句可以有一个可选label来命名switch块。 此名称可用于嵌套的switch break语句，以打破封闭的开关，而不仅仅是拥有的开关。

开关标签仅用于命名块，标签名称必须是带有单个或多个单词的双引号常量字符串。 label关键字区分大小写，应写为label 。

语法 (Syntax)

简单switch...label的语法switch...label语句如下 -

switch expression label "Label Name" do
   case <val> [, <val-1>....] then
      -- Executes when the expression matches one of the values
      break "LEBEL NAME" 
   case <val> [, <val-1>....] then
      -- Executes when the expression matches one of the values 
      break "LEBEL NAME"  
      .....................
   case else
      -- Executes when the expression does not matches any case.
      break "LEBEL NAME"   
end if

例子 (Example)

#!/home/euphoria-4.0b2/bin/eui
atom marks = 'C'
atom scale = 'L'
switch marks label "MARKS" do
   case 'A' then
      puts(1, "Excellent!\n" )
   case 'B', 'C' then
      puts(1, "Well done!\n" )
      switch scale label "SCALE" do
         case 'U' then
             puts(1, "Upper scale!\n" )
             break "MARKS"
         case 'L' then
             puts(1, "Lower scale!\n" )
             break "MARKS"
         case else
             puts(1, "Invalid scale!\n" )
             break "MARKS"
      end switch
   case 'D' then
      puts(1, "You passed!\n" )
   case 'F' then
      puts(1, "Better try again!\n" )
   case else
      puts(1, "Invalid grade!\n" )
end switch

这会产生以下结果 -

Well done!
Lower scale!

Note - 如果您没有使用with fallthru语句，那么您不需要使用标签，因为switch语句会自动出现。