c# - C# 中的选项与 SQL 中的 'IN' 具有相同的功能？

Question

我想在 if 条件 block 中搜索多个条件 - 就像 SQL 中的 IN 运算符一样。

public class Check{

    int [] arr = {1, 2, 5, 9, 7, 11, 89};
    for (int i=0; i<arr.length; i++)
    {
      if(arr[i]==1||arr[i]==5||arr[i]==7||arr[i]==89)
      {
        Console.WriteLine("The number was found.");
      }
    }

Is there a solution for this kind of result?

if (arr[i] in(1, 5, 7, 89)
{
    Console.WriteLine("The No Is Found.");
}

Answer 1

作为一种语言，C# 中没有任何东西等同于IN。 , 不...但你可以轻松实现类似的效果。

最简单的方法可能是使用 System.Linq和 Contains针对数组:

using System;
using System.Linq;

public class Check{

    static void Main()
    {
        int[] candidates = {1, 2, 5, 9, 7, 11, 89};
        // This is the members of the "in" clause - the
        // the values you're trying to check against
        int[] targets = { 1, 5, 7, 89 };
        foreach (int candidate in candidates)
        {
            Console.WriteLine(
                targets.Contains(candidate) ?
                $"{candidate} is in targets" :
                $"{candidate} is not in targets");
        }
    }
}

或者，您可以使用 HashSet<int> - 如果你有大量的目标，那会更有效率:

using System;
using System.Collections.Generic;

public class Check{

    static void Main()
    {
        int[] candidates = {1, 2, 5, 9, 7, 11, 89};
        var targets = new HashSet<int> { 1, 5, 7, 89 };
        foreach (int candidate in candidates)
        {
            Console.WriteLine(
                targets.Contains(candidate) ?
                $"{candidate} is in targets" :
                $"{candidate} is not in targets");
        }
    }
}