对象编程

Week 2

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

namespace ConsoleApp1
{
    internal class Program
    {
        static void Main(string[] args)
        {
            double a = 5.456;
            int b = 15;
            Console.WriteLine(a);
            Console.WriteLine("Hello world {1} {0}", a, a + b); // 先填小的0再填大的1, 没有0只有1直接报错
            Console.WriteLine("{0, 4:f2}", a);
            Console.WriteLine($"Hello world {a} {a + b}");
            //string str = Console.ReadLine(); // 只能用string
            string str = "15 65 8 96";
            Console.WriteLine(str);
            //double ans = Convert.ToDouble(str); // 转换成double
            String[] result = str.Split(' ',',');
            foreach (string s in result) {
              Console.WriteLine($"{Convert.ToInt32(s)}");
            }
            int[] sum = Array.ConvertAll(result, Convert.ToInt32);
            foreach (int s in sum)
            {
                Console.WriteLine("{0}", s);
            }

            char flag = '5';
            Console.WriteLine(char.IsNumber(flag));
            string s1 = "Hello ";
            string s2 = "World!";
            string s3 = s1 + s2;
            Console.WriteLine(s3[7] + s2[2]);//只读不能改
            Console.WriteLine("a" + 300 + 5 + "b");
            Console.WriteLine("a" + (300 + 5) + "b");

            string s4 = "nihao\nnihao";
            Console.WriteLine(s4);
            s4 = @"nihao\nnihao"; //@符号表示逐字字符串，\n不再被解释为换行符，而是作为普通的文本输出
            Console.WriteLine(s4);

            string s5 = "World!";
            Console.WriteLine(s2 == s5);//C#中字符串比较是比较内容而不是地址

            double d1 = 1.5;
            float d2 = 1.0f;//必须有f否则报错,因为double精度高, C#的默认浮点数类型是double且不支持隐式转换为float
            decimal x = (decimal)d1;//显式转换

            int k1= Convert.ToInt32("48");
            int k2 = int.Parse("45"); // Convert.ToInt32和int.Parse的区别：Convert.ToInt32在转换失败时返回0，而int.Parse会抛出异常

            int res;
            bool q = int.TryParse("abc", out res); // TryParse方法尝试将字符串转换为整数，如果转换成功返回true，并将结果存储在res中；如果转换失败返回false，并将res设置为0
            Console.WriteLine($"q is {q}, res is {res}");
        }
    }
    public enum Title { 
        apple,
        banana,
        orange, //用逗号,默认是int
    }
    public class Student
    {
        public string name;
        public int age;
        public Title title;
        public Student(string name, int age) {
            this.name = name;
            this.age = age;
        }
        public void sum() {
            switch (title)
            {
                case Title.apple:
                    Console.WriteLine("apple");
                    break;
                case Title.banana: 
                    Console.WriteLine("banana");
                    break;
                case Title.orange:
                    Console.WriteLine("orange");
                    break;
            }
        }
    }
}