C# 程序使用 LINQ 的 where() 方法查找姓名以“S”开头的学生列表

LINQ 被称为语言集成查询，它是在 .NET 3.5 中引入的。它使.NET语言能够生成查询以从数据源中检索数据。它消除了编程语言和数据库之间的不匹配，并且无论使用哪种类型的数据源，用于创建查询的语法都是相同的。在本文中，我们将学习如何使用 List Collection 的 where() 方法打印姓名以“S”开头的学生列表。这里的 where 方法根据谓词过滤给定的值序列或数组。要使用 where() 方法，您需要在程序中导入System.Linq和System.Collections.Generic命名空间。

句法：

Where(IEnumerable, Func)

例子：

Input : List of Students:
        {{id = 101, name = "Sravan", age = 12},
         {id = 102, name = "deepu",  age = 15},
         {id = 103, name = "manoja", age = 13},
         {id = 104, name = "Sathwik", age = 12},
         {id = 105, name = "Saran",  age = 15}}
Output: {{id = 105, name = "sravan", age = 15},
         {id = 104, name = "Sathwik",age = 12},
         {id = 105, name = "Saran",  age = 15}}
     
Input: List of Students:
       {{id = 102, name = "deepu",  age = 15},
        {id = 103, name = "manoja", age = 13}}
Output: No Output

方法：

To find the list of students whose name starts with ‘S’ follow the following steps:

1. Create a list of students with three variables(Id, name and age).
2. Iterate through the student details by using Where() function and get the student details by choosing student name starts with’ S’ using s => s.name[0] == ‘S’.
3. Now call the ToString() method.
4. Display the student details.

例子：

C#

// C# program to display the list of students whose 
// name starts with 'S'. Using Where() function 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
  
class Student{
      
// Declare 3 variables - id, age and name
int id; 
int age;
string name;
  
// Get the to string method that returns 
// id , name and age
public override string ToString()
{
    return id + " " + name + " " + age;
}
  
// Driver code
static void Main(string[] args)
{
      
    // Declare a list variable 
    List student = new List()
    {
          
        // Create 5 Student details
        new Student{ id = 101, name = "Sravan", age = 12  },
        new Student{ id = 102, name = "deepu", age = 15 },
        new Student{ id = 103, name = "manoja", age = 13 },
        new Student{ id = 104, name = "Sathwik", age = 12 },
        new Student{ id = 105, name = "Saran", age = 15 }
      
    };
      
    // Iterate the Student by selecting Student 
    // name starts with S
    // Using Where() function
    IEnumerable Query = student.Where(s => s.name[0] == 'S');
      
    // Display employee details
    Console.WriteLine("ID  Name  Age");
    Console.WriteLine("+++++++++++++");
    foreach (Student e in Query)
    {
          
        // Call the to string method
        Console.WriteLine(e.ToString());
    }    
}
}

输出：

ID  Name  Age
+++++++++++++
101 Sravan 12
104 Sathwik 12
105 Saran 15