C＃if語句！=多個值的

Question

Console.Clear(); 
string choice; 

Console.WriteLine("Welcome to Costa coffee\n"); 
Console.WriteLine("1:> Latte\n2:> Cappuccino\n3:> Espresso\n4:> Double espresso"); 
Console.WriteLine("\nPlease select a coffee by pressing 1-4"); 
choice = Console.ReadLine(); 


if (choice == "1") 
{ 
    Console.WriteLine("\nYou have selected: latte"); 
} 
if (choice == "2") 
{ 
    Console.WriteLine("\nYou have selected: Cappuccino"); 
} 
if (choice == "3") 
{ 
    Console.WriteLine("\nYou have selected: Espresso"); 
} 
if (choice == "4") 
{ 
    Console.WriteLine("\nYou have selected: Double espresso"); 
} 

else if (choice !="1" || choice !="2" || choice !="3" || choice !="4") 
{ 
    Console.WriteLine("Incorrect value, please try again"); 
} 

我試圖讓程序，如果選擇不等於1,2,3,4那麼它會顯示「不正確的值，請再試一次」然而，當我按下任何東西時仍然有效，但在按1,2,3或4時仍然顯示此錯誤消息。任何想法？

Answer 1

您的前三條if語句與最後兩條語句無關。您應該在if for choice == 2和choice == 3之前添加else。這樣，這一切都成爲一個大的if/else語句。

Answer 2

中平凡調整你的代碼（但有更好的方法來寫）：

Console.Clear(); 
string choice; 

Console.WriteLine("Welcome to Costa coffee\n"); 
Console.WriteLine("1:> Latte\n2:> Cappuccino\n3:> Espresso\n4:> Double espresso"); 
Console.WriteLine("\nPlease select a coffee by pressing 1-4"); 
choice = Console.ReadLine(); 


if (choice == "1") 
{ 
    Console.WriteLine("\nYou have selected: latte"); 
} 
else if (choice == "2") 
{ 
    Console.WriteLine("\nYou have selected: Cappuccino"); 
} 
else if (choice == "3") 
{ 
    Console.WriteLine("\nYou have selected: Espresso"); 
} 
else if (choice == "4") 
{ 
    Console.WriteLine("\nYou have selected: Double espresso"); 
} 
else 
{ 
    Console.WriteLine("Incorrect value, please try again"); 
} 

Answer 3

推薦switch在這種情況下：

var myConsoleString = ""; 

switch (choice) 
{ 
    case "1": myConsoleString = "\nYou have selected: latte"; break; 
    case "2": myConsoleString = "\nYou have selected: Cappuccino"; break; 
    case "3": myConsoleString = "\nYou have selected: Espresso"; break; 
    case "4": myConsoleString = "\nYou have selected: Double espresso"; break; 
    default: myConsoleString = "\nIncorrect value, please try again"; break; 
} 

Console.WriteLine(myConsoleString); 

Answer 4

幹版：

var coffee = null; 

switch (choice) 
{ 
    case "1": coffee = "Latte"; break; 
    case "2": coffee = "Cappuccino"; break; 
    case "3": coffee = "Espresso"; break; 
    case "4": coffee = "Double espresso"; break; 
} 

Console.WriteLine(coffee == null ? "Incorrect value, please try again" : $"You have selected: {coffee}"); 

Answer 5

在你的代碼有兩件事是錯誤的：

1. else if塊只在choice == "4"失敗時執行，如果所有條件都失敗，您希望它運行。
2. 條件本身不檢查你真的想檢查什麼，你想顯示錯誤消息，如果選擇不是1 和沒有2 和沒有3 和沒有4.但是，您正在使用或運算符。所以你可以通過使用AND來解決這個問題，但是它不能解決整個問題，反正它不是一個好的解決方案。

你需要的是一個如果 - 否則，如果 - 其他結構，而不是連續如果的。

if (choice == "1") 
{ 
    Console.WriteLine("\nYou have selected: latte"); 
} 
else if (choice == "2") 
{ 
    Console.WriteLine("\nYou have selected: Cappuccino"); 
} 
else if (choice == "3") 
{ 
    Console.WriteLine("\nYou have selected: Espresso"); 
} 
else if (choice == "4") 
{ 
    Console.WriteLine("\nYou have selected: Double espresso"); 
} 
else 
{ 
    Console.WriteLine("Incorrect value, please try again"); 
} 

這比if的鏈更好，因爲其他條件只會在條件失敗之前被評估。例如，如果choice == "2"如果choice == "1"爲真沒有意義。如果所有的條件都失敗了，那麼else塊將被執行，這是你首先想要的。請注意，沒有必要編寫一個與所有條件相反的條件，因此有一個else語句用於此目的。

Answer 6

我討厭重複我自己，所以我會以減少重複的方式來解決這個問題。

通過使有效選項的字典，生成消息的邏輯變得更清晰，新方案的加入是其選擇作出決定的邏輯不太交織：

var possibleChoices = new Dictionary<string,string>{ 
    {"1", "Latte"}, 
    {"2", "Cappuccino"}, 
    {"3", "Espresso"}, 
    {"4", "Double espresso"} 
}; 

string value; 

var message = possibleChoices.TryGetValue(choice, out value) 
    ? string.Format("You have selected: {0}", value) 
    : "Incorrect value, please try again"; 

//In your code, the fall-through case misses the leading \n . 
//By avoiding repetition, consistency in formatting is achieved 
//with a single line of code 
Console.WriteLine("\n{0}", message); 

Answer 7

你可以使用字典讓事實「1」是「拿鐵」和其他值更具體，這將允許您使用.Contains()方法，以替代多個if的或switch聲明：

Console.Clear(); 
string choice; 
Dictionary<string, string> choiceToCoffee = new Dictionary<string, string>() 
{ 
    { "1", "Latte" }, 
    { "2", "Cappuccino" }, 
    { "3", "Espresso" }, 
    { "4", "Double Espresso" }, 
}; 
Console.WriteLine("Welcome to Costa coffee\n"); 
foreach (var kvp in choiceToCoffee) 
{ 
    var thisChoice = kvp.Key; 
    var thisCoffee = kvp.Value; 
    Console.WriteLine(thisChoice + ":> " + thisCoffee); 
} 
Console.WriteLine("\nPlease select a coffee by pressing 1-4"); 
choice = Console.ReadLine(); 

if (choiceToCoffee.ContainsKey(choice)) 
{ 
    Console.WriteLine("\nYou have selected: " + choiceToCoffee[choice]); 
} 
else 
{ 
    Console.WriteLine("Incorrect value, please try again"); 
}