csharp C＃ - 教程003 - 异常时的条件

Posted 2021-05-12

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

namespace CSharpTutA.cs
{
    class Program
    {
        
        static void Main(string[] args)
        {
            // ----- CONDITIONALS -----
            // ----- IF / ELSE / -----
            // Relational Operators : > < >= <= == !=
            // Logical Operators : && || !

            int age = 17;

            if ((age >= 5) && (age <= 7))
            {
                Console.WriteLine("Go to elementary school");
            }
            else if ((age > 7) && (age < 13))
            {
                Console.WriteLine("Go to middle school");
            }
            else if ((age > 13) && (age < 19))
            {
                Console.WriteLine("Go to high school");
            }
            else
            {
                Console.WriteLine("Go to college");
            }

            if ((age < 14) || (age > 67))
            {
                Console.WriteLine("You shouldn't work");
            }

            Console.WriteLine("! true = " + (!true));

            // Ternary Operator
            // Assigns the 1st value if true and otherwise 
            // the 2nd
            bool canDrive = age >= 16 ? true : false;

            // Switch is used when you have limited options
            // The only way to use ranges is to stack 
            // the possible values
            switch (age)
            {
                case 1:
                case 2:
                    Console.WriteLine("Go to Day Care");
                    break;
                case 3:
                case 4:
                    Console.WriteLine("Go to Preschool");
                    break;
                case 5:
                    Console.WriteLine("Go to Kindergarten");
                    break;
                default:
                    Console.WriteLine("Go to another school");
                    // You can also jump out of a switch
                    // with goto
                    goto OtherSchool;
            }

            OtherSchool:
            Console.WriteLine("Elementary, Middle, High School");

            // To compare strings use Equals
            string name = "Derek";
            string name2 = "Derek";

            if (name.Equals(name2, StringComparison.Ordinal))
            {
                Console.WriteLine("Names are Equal");
            }

            // ----- WHILE LOOP -----
            // You use the while loop when you want to execute
            // as long as a condition is true

            // This while loop will print odd numbers between
            // 1 and 10
            int i = 1;
            while (i <= 10)
            {
                // % (Modulus) returns the remainder of a
                // division. If it returns 0 that means the
                // value is even
                if (i % 2 == 0)
                {
                    i++;

                    // Continue skips the rest of the code and 
                    // starts execution back at the top of the 
                    // while
                    continue;
                }

                // Break jumps completely out of the loop
                if (i == 9) break;

                Console.WriteLine(i);
                i++;
            }

            // ----- DO WHILE LOOP -----
            // Use do while when you must execute the code
            // at least once

            // Generate a random number
            Random rnd = new Random();
            int secretNumber = rnd.Next(1, 11);
            int numberGuessed = 0;

            do
            {
                Console.Write("Enter a number between 1 & 10 : ");

                // Use Convert to switch the string into an int
                numberGuessed = Convert.ToInt32(Console.ReadLine());

            } while (secretNumber != numberGuessed);

            Console.WriteLine("You guessed it is was {0}",
                secretNumber);

            // Other Convert options : ToBoolean, ToByte,
            // ToChar, ToDecimal, ToDouble, ToInt64,
            // ToString, and they can convert from any 
            // type to any other type

            // ----- EXCEPTION HANDLING -----
            // We use exception handling to catch errors
            // that could crash our program
            double num1 = 5;
            double num2 = 0;

            // Code that could cause an error is surrounded
            // by a try block
            try { 
            Console.WriteLine("5 / 0 = {0}", 
                DoDivision(num1, num2));
            }

            // We catch the error and warn the user 
            // rather then crash the program
            catch (DivideByZeroException ex)
            {
                Console.WriteLine("You can't Divide by Zero");

                // Get additonal info on the exception
                Console.WriteLine(ex.GetType().Name);
                Console.WriteLine(ex.Message);

            }

            // This is the default catch all for exceptions
            catch (Exception ex)
            {
                Console.WriteLine("An error occurred");
                Console.WriteLine(ex.GetType().Name);
                Console.WriteLine(ex.Message);
            }

            // finally always runs and provides for clean up
            finally
            {
                Console.WriteLine("Cleaning Up");
            }

            // Well cover more about exception handling 
            // with some real examples soon

            Console.ReadLine();

        }

        static double DoDivision(double x, double y)
        {
            if(y == 0)
            {
                // We are throwing an exception because
                // you can't divide by zero
                throw new System.DivideByZeroException();
            }
            return x / y;
        }

    }
}