为什么 C# 中存在未处理的异常错误？

Question

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

namespace HelloWorld
{
public class Program
{
public static void Main(string[] args)
{
  int a, b, c;
 Console.WriteLine("give a:");
 a=int.Parse(Console.ReadLine());
 Console.WriteLine("give b:");
 b=int.Parse(Console.ReadLine());
  
  c=a+b;
  Console.WriteLine("c={0}",c);
} 
}
}

The error is this :

Unhandled Exception:
System.ArgumentNullException: Value cannot be null.
Parameter name: s
  at System.Int32.Parse (System.String s) [0x00003] in <9f0df102fe6e4cfea29d2e46f585d8a5>:0 
  at HelloWorld.Program.Main (System.String[] args) [0x00011] in <47cc63d67af642a680e3be47ee0a2658>:0 
[ERROR] FATAL UNHANDLED EXCEPTION: System.ArgumentNullException: Value cannot be null.
Parameter name: s
  at System.Int32.Parse (System.String s) [0x00003] in <9f0df102fe6e4cfea29d2e46f585d8a5>:0 
  at HelloWorld.Program.Main (System.String[] args) [0x00011] in <47cc63d67af642a680e3be47ee0a2658>:0

Why does this error appear?

I'm using a mobile compiler.

Is it because there are 2 inputs and the mobile compiler can't handle more than one input?

Or is it an error in the code?

Answer 1

It's certainly a conundrum. Online compilers can be a bit iffy. I've just tried the following code on TutorialsPoint.com

/* Online C# Compiler and Editor */
using System.IO;
using System;

namespace HelloWorld
{
    public class Program
    {
        public static void Main(string[] args)
        {
            int a, b, c;
            Console.WriteLine("give a:");
            a=int.Parse(Console.ReadLine());
            Console.WriteLine("give b:");
            b=int.Parse(Console.ReadLine());
  
            c=a+b;
            Console.WriteLine("c={0}",c);
        } 
    }
}

And it works:

Output:

give a:
1
give b:
2
c=3

edit

Inclusion of my remark and thinking behind it to the original question:

Your original error message:

Parameter name: s at System.Int32.Parse (System.String s) [0x00003] in <9f0df102fe6e4cfea29d2e46f585d8a5>:0 at HelloWorld.Program.Main (System.String[] args) [0x00011] in <47cc63d67af642a680e3be47ee0a2658>:0

indicates that there is a parameter called s . Perhaps the online compiler that you used recognises arg but not args and so sees the s as a parameter of an unknown type. Try arg instead of args