98 lines
2.4 KiB
Markdown
98 lines
2.4 KiB
Markdown
---
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title: If
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localeTitle: 如果
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---
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# 如果
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if语句根据条件执行不同的代码块。
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```
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if (condition)
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{
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// Do something when `condition` is true
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}
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else
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{
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// Do something when `condition` is false
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}
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```
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当`condition`为真，代码里面`if`部分执行，否则`else`执行。有时您需要添加第二个条件。为了便于阅读，您应该使用`else if`而不是嵌套`if`语句。 而不是写：
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```
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if (condition)
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{
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// Do something if `condition` is true
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}
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else
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{
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if (anotherCondition)
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{
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// Do something if `anotherCondition` is true
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}
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else
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{
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// Do something if `condition` AND `anotherCondition` is false
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}
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}
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```
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你可以使用更简洁的写作：
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```
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if (condition)
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{
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// Do something if `condition` is true
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}
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else if (anotherCondition)
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{
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// Do something if `anotherCondition` is ture
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}
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else
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{
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// Do something if `condition` AND `anotherCondition` is false
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}
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```
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还可以检查条件是否为假并在不必具有else语句的情况下对其进行操作。
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```
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if(!condition)
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{
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//do something if the condition is false
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}
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```
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```
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int number = 3;
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//!= implies that you wish to check if the object's value is not equal to the value next to it
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if(number !=2)
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{
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Console.WriteLine("Number is not 2");
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}
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```
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请注意， `else`和`else if`部分不是必需的，而`if`是必需的。
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## 例
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```
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Console.WriteLine("Who are you? ");
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string name = Console.ReadLine();
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if (name == "John")
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{
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Console.WriteLine("Hi John!");
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}
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else if (name == "Fabio")
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{
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Console.WriteLine("Oh, it's you Fabio :)");
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}
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else
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{
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Console.WriteLine("Oh! I thought you were John or Fabio. Anyway, nice to meet you {0}!", name);
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}
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/* Run and type some names:
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-> If name is "John", then output is "Hi John!"
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-> If name is "Fabio", then output is "Oh, it's you Fabio :)"
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-> If name is neither "John" nor "Fabio", output is "Oh! I thought you were John or Fabio. Anyway, nice to meet you {0}!" where {0} contains the name.
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*/
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```
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if语句需要一个布尔结果，即true或false。在某些编程语言中，几种数据类型可以自动转换为布尔值，但在C＃中，您必须专门将结果设置为布尔值。例如，你不能使用if（number），但你可以将数字与某些东西进行比较，以生成true或false。 |