Is there a way to fix my program to resolve 'Converting null Literal to non-nullable type' in C#?

Question

My goal in this program is to allow the user to change the values in a operation and find the area(basically useless calculator) of the rectangle. The results i would expect(from python exp.) is that is woulld read the line and convert it into int, then i could multiply the two variables to get the area. Whenever I have tried this, the Error CS8600('Converting null literal to non-nullable type') in line 10(string name = Console.ReadLine();) I first thought that it could be some problem with the conversion to integer(Spare me, i am very new to this language and Object Oriented Programming in general.) I have not found solutions that i can understand online and am resorting to Stack Overflow. Here's the code, please help me:


namespace world
{
    class Username
    {
        static void Main(string[] args)/* by accident i wrote public*/
        {
            Console.WriteLine("What is your name? ");
            string name = Console.ReadLine();
            Console.WriteLine("Your name is " + name);
            Console.WriteLine("Now about rectangles...");
            Console.WriteLine("Length = ");
            string inlength = Console.ReadLine()??string.Empty;
            int length;
            Int32.TryParse(inlength, out length);
            Console.WriteLine("Width = ");
            string inwidth = Console.ReadLine()??string.Empty;
            int width;
            Int32.TryParse(inwidth, out width);
            int area = length * width;
            Console.WriteLine(area);


        }
    }
}

You probably have settings so that nullability must be handled. You could turn that off (project settings, I think) or you will have to mark the string as nullable since `Console.ReadLine()` may return a null. — Sami Kuhmonen, Apr 08 '22 at 15:31
I am using VS code in mac, how can i locate this @SamiKuhmonen — JebKerman, Apr 08 '22 at 15:34
No need to disable nullable reference types. That would not solve the underlying problem that `Console.ReadLine` could return null. Replace `var inlength = Console.ReadLine();` by `string inlength = Console.ReadLine()??string.Empty;`. Of course you could still get exceptions trying to parse the inut to an integer if invalid input is given. — Johan Donne, Apr 08 '22 at 15:38
@JohanDonne the error is still being given in ```string name = Console.ReadLine();``` in line 10. Same error — JebKerman, Apr 08 '22 at 15:48
In terminal the terminal just doesn't want to to do the part after "what is your name — JebKerman, Apr 08 '22 at 15:55
You have NOT edited `string name = Console.ReadLine();` which where the error is. — Poul Bak, Apr 08 '22 at 16:19
@PoulBak y'all missed the 'public void' instead of 'static void' — JebKerman, Apr 09 '22 at 03:48

score 2 · Answer 1 · answered Apr 08 '22 at 16:10

null in C# is similar (though far from identical) to null in other languages like JavaScript or None in Python.
Your string name statement declares a variable named name of type non-nullable System.String
- The string keyword in C# is an alias for the System.String type.
However, the Console.ReadLine() method has a return-type of nullable System.String (i.e. string?).
- Console.ReadLine() returns null if a user presses Ctrl + Z in a Windows console window.
Therefore, you need to consider how your program will behave in the event the user presses Ctrl + Z while at the "What is your name?" prompt.
The quick-fix is to disregard Ctrl + Z input and treat it the same as empty-input, in which case the use of ?? String.Empty (or just ?? "") is perfectly fine, and is what you're already doing in the rest of your program already.

You all missed the 'public void' instead of 'static void' () — JebKerman, Apr 09 '22 at 03:47
@JebKerman `static void` is fine. Non-static `public void` won’t work: `Main` must be static. — Dai, Apr 09 '22 at 05:18

Is there a way to fix my program to resolve 'Converting null Literal to non-nullable type' in C#?

1 Answers1