C# if语句

if语句根据条件执行不同的代码块。

if (condition)
{
  // Do something when `condition` is true
}
else
{
  // Do something when `condition` is false
}

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：

if (condition)
{
  // Do something if `condition` is true
}
else
{
  if (anotherCondition)
  {
      // Do something if `anotherCondition` is true
  }
  else
  {
      // Do something if `condition` AND `anotherCondition` is false
  }
}

你可以使用更简洁的写作：

if (condition)
{
  // Do something if `condition` is true
}
else if (anotherCondition)
{
  // Do something if `anotherCondition` is ture
}
else
{
  // Do something if `condition` AND `anotherCondition` is false
}

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。

if(!condition)
{
//do something if the condition is false
}

int number = 3;
//!= implies that you wish to check if the object's value is not equal to the value next to it
if(number !=2)
{
   Console.WriteLine("Number is not 2");
}

请注意， else和else if部分不是必需的，而if是必需的。

例

Console.WriteLine("Who are you? ");
string name = Console.ReadLine();

if (name == "John")
{
    Console.WriteLine("Hi John!");
}
else if (name == "Fabio")
{
    Console.WriteLine("Oh, it's you Fabio :)");
}
else
{
    Console.WriteLine("Oh! I thought you were John or Fabio. Anyway, nice to meet you {0}!", name);
}

/* Run and type some names:
    -> If name is "John", then output is "Hi John!"
    -> If name is "Fabio", then output is "Oh, it's you Fabio :)"
    -> 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.
*/

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。

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