Abstract Class, C#

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//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public abstract class absParentClass  
    //public class absParentClass
    {
        //public abstract int addition(int a, int b)  --> Error, cannot declare a body because it is marked abstract
        //{
          // Console.WriteLine(a+b);
          //  return a+b;
        //}
        public int addition(int a, int b)  
        {
         Console.WriteLine(a+b);
          return a+b;
        }
        public int sub(int a, int b)  
        {
         Console.WriteLine(a-b);
          return a+b;
        }
        public abstract int mul(int a,int b);
        public abstract int div(int a,int b);
    }
    
    public class absChildClass: absParentClass
        
    {
         //Before Call Parent Class methods addition and sub , We must implement abstract parent methods under child class.
        public override int mul(int a, int b)  
        {
         Console.WriteLine(a*b);
          return a+b;
        }
        public override int div(int a, int b)  
        {
         Console.WriteLine(a/b);
          return a+b;
        }
    }
    
    public class Program
    {
        public static void Main(string[] args)
        {
            //Your code goes here
            Console.WriteLine("Hello, world!");
            
            //--> Cannot create an instance of the abstract class or interface absParentClass
            //absParentClass apc=new absParentClass(); 
            //apc.addition(3,5);
                
            absChildClass acc=new absChildClass();
            acc.addition(2,3);
            acc.sub(4,1);
            acc.mul(3,5);
            acc.div(20,4);
            
            //--> Call the all methods with the reference of Parent Abstract Class.
            absParentClass apc =acc;
            apc.addition(2,8);
            apc.sub(4,1);
            apc.mul(2,3);
            apc.div(10,2);
        }
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,19 sec, absolute running time: 0,13 sec, cpu time: 0,12 sec, average memory usage: 15 Mb, average nr of threads: 3, absolute service time: 0,36 sec