使用變量作爲SWICH聲明case常量

Question

我試圖用一個變量的情況下比賽，但是我得到「表情不是Objective-C的整數。

是否有可能在交換機中使用變量以這種方式？

int count = [array count]; 

    switch ([number to check]) { 
     case 0: 
      //first statement 
      break; 
     case 1 ... (count -1): 
      //somewhere between 1 and the next to last statement 
      //Basically the middle 
      break; 
     case count: 
      //Last statement 

     default: 
      break; 
    } 

Answer 1

的Objective-C（和C）switch只支持每個case語句（如在由TwoStraws回答指出或範圍）的單個原始的恆定值。你會好得多使用if/else編寫代碼：

if ([number to check] == 0) { 
} else if ([number to check] >= 1 && [number to check] < count) { 
} else if ([number to check] == count) { 
} else { 
} 

Answer 2

Objective-C的switch語句支持您所看到的值範圍，但不支持變量匹配。

int numberOfKittens = 12; 
NSString *kittenDescription; 

switch (numberOfKittens) { 
    case 0 ... 5: 
     kittenDescription = @"Need more kittens"; 
     break; 

    case 6 ... 10: 
     kittenDescription = @"That's a good number of kittens."; 
     break; 

    case 11 ... 20: 
     kittenDescription = @"Are you sure you can handle that many kittens?"; 
     break; 

    default: 
     kittenDescription = @"You must really love kittens!"; 
} 

...但試圖把一個變量代替任何這些將失敗：

所以，因爲我已經用準確的整數下面的代碼是有效的。

如果這是你非常想要的東西，可以考慮使用Swift，因爲它具有更具表達力的switch匹配系統。下面是斯威夫特同樣的代碼，現在用一個變量用來匹配情況：

let upperLimit = 20 
let numberOfKittens = 19 
var kittenDescription = "" 

switch (numberOfKittens) { 
case 0 ... 5: 
    kittenDescription = "Need more kittens" 

case 6 ... 10: 
    kittenDescription = "That's a good number of kittens." 

case 11 ... upperLimit: 
    kittenDescription = "Are you sure you can handle that many kittens?" 

default: 
    kittenDescription = "You must really love kittens!" 
}