how to make user input int null value c#

Question

I'm trying to make a program that takes a number and print it on screen but if the user press enter the code ask the user to enter the number again but instead it shows me a exception

Enter_No:
                 Console.WriteLine("enter number");
                 int? n = Convert.ToInt32(Console.ReadLine());
                 if (n == (int?)null)
                 {
                     goto Enter_No;
                 }
                 else
                 {
                     Console.WriteLine(n);
                 } 

Answer 1

Use int.TryParse :

int? num = null;
while(!num.HasValue)
{
    Console.WriteLine("Please enter an integer:");
    num = int.TryParse(Console.ReadLine(), out int i) ? i : new int?();
}

Console.WriteLine("Entered integer: " + num.Value);

Answer 2

Tim's solution is wonderfully compact. Here's why your attempt failed.

From MSDN , Convert.ToInt32() throws a FormatException if:

value does not consist of an optional sign followed by a sequence of digits (0 through 9).

The preferred approach is int.TryParse() , as it returns false if it's unable to parse the integer rather than throwing an exception.

While the goto keyword is supported in C#, there are few or no situations (depending on who you ask) where it's the best option for flow control. Tim's while loop is an excellent approach.

Answer 3

First, don't use Go To:

Second: Inspect your data and use tryparse:

        bool success = false;
        do
        {
            Console.WriteLine("enter number");
            var n = Console.ReadLine();
            if (n == null)
            {
                // goto Enter_No;
            }
            else
            {
                int typedNum;
                success = int.TryParse(n, out typedNum);
                Console.WriteLine(typedNum);                    
            }
        } while (!success);