1.基础查询linq

1.基本查询语法，查询所有偶数

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] arr = { 5,8,10,13,29,18,6};
            var nums = from n in arr
                       where n % 2 == 0
                       select n;  //查询所有偶数
            foreach(int n in nums)//遍历查询结果
            {
                Console.WriteLine("偶数：{0}",n);
            }
        }
    }
运行结果：
}

2.查询所有偶数并倒序排序，即：从大到小排using System;using System.Collections.Generic;

using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] arr = { 5,8,10,13,29,18,6};
            var nums = from n in arr
                       where n % 2 == 0
                       orderby n  descending //查询所有偶数并倒序排序，就是从大到小排序。
                       select n;  //查询所有偶数
            foreach(int n in nums)//遍历查询结果
            {
                Console.WriteLine("偶数：{0}",n);
            }
        }
    }
}
运行结果：

4.投影新对象

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
    class Student {
        public string Name { get; set; }
        public string Sex { get; set; }
        public int Age { get; set; }
    }
    class Program
    {
        static void Main(string[] args)
        {

            //使用对象初始化器和集合初始化器来实例化学生列表
            List<Student> listStu = new List<Student>();
            {
                new Student(){Age=18,Name="莉莉",Sex="女"};
                 new Student(){Age=17,Name="小米",Sex="女"};
                 new Student() { Age = 28, Name = "小刚", Sex = "女" };

            };
            //查询并投影新对象，使用动态类型变量声明符和对象初始化器
            var stus= from stu in listStu
                      where stu.Age > 17
                      select new { StName=stu.Name,Stutex=stu.Sex};
            //遍历新对象集合，并输出新对象的属性
            foreach (var st in stus)
            {
                Console.WriteLine("{0},{1}",st.StName, st.Stutex);

            }
        }
    }
}

 

5.获取集合对象的，长度大于7对象。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {

            string[] arr = { "shenzhen","xian","nanjing","shanghai"};
            IEnumerable<string> strs = from s in arr
                                       where s.Length > 7  
                                       select s; //获取对象集合
            foreach (var s in strs)  //循环对象
            {
                Console.WriteLine(s);
            }

        }
    }
}
运行结果：