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

namespace WindowsDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            //调用外部函数
            subStringDemo();
        }
        //取子字符串函数
        static void subStringDemo()
        {
            string str = "123456";
            string subStr1 = str.Substring(5);
            string subStr2 = str.Substring(0, 5);
            Console.WriteLine("单个参数: " + subStr1);
            Console.WriteLine("两个参数: " + subStr2);
            Console.ReadKey();
        }
    }
}

String str=”123456”;

subStr=str.Substring(2,5);

System.Output.println(subStr);

//输出结果

345