Getting "Input string was not in a correct format." on SECOND step thru loop

Question

Code enclosed below. I am coding a menu where the user types a number to select a menu option. It also is enclosed in a while loop, so the user can repeat the menu over and over again. It works perfectly on the first loop thru, but on the second it gives "Input string was not in a correct format." at the Console.ReadLine()

static void Main(string[] args)
    {
        bool again = true;
        while (again)
        {

            string yourName = "Someone";

            Console.WriteLine("\t1: Basic Hello, World.\n" +
                "\t2: Calculate demoninations for a given value of change.\n" +
                "\t3: Calculate properties of shapes.\n" +
                "Please Select an Option: ");
            int option = int.Parse(Console.ReadLine());//errors out here.
            switch (option)
            {

            }
            Console.Write("Press y to back to the main menu.  Press any other key to quit: ");
            char againChoice = (char)Console.Read();
            if (againChoice == 'y')
            { again = true; }
            else
            { again = false; }
        }
        Console.Write("Hit Enter to end");
        Console.Read();
    }

Damith · Answer 1 · 2015-05-30T18:28:46.807

1

int.TryParse is better method than int.Parse when you not sure about input value entered by the user

int option;
if(int.TryParse(Console.ReadLine(), out option))
{
  switch (option)
  {

  }
}
Console.Write("Press y to back to the main menu.  Press any other key to quit: ");
char againChoice = (char)Console.Read();
// also add read line to capture enter key press after press any key
Console.ReadLine();

or change the back menu code as

string againChoice = Console.ReadLine();
again =againChoice == "y";

edited May 30 '15 at 18:28

answered May 30 '15 at 18:08

Damith

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You kind of gloss over it but the real main fix is the `Console.ReadLine();` you added. – Scott Chamberlain May 30 '15 at 18:19
Thank you. This wasn't quite the answer I was looking for, but you've given me a lot to think about. – Will May 31 '15 at 02:39

score 1 · Accepted Answer · answered May 30 '15 at 18:29

    int option = int.Parse(Console.ReadLine());

Focus on writing debuggable code:

    string input = Console.ReadLine();
    int option = int.Parse(input);

Now you can use the debugger, set a breakpoint on the Parse() statement. And you'll easily see why the Parse() method threw an exception. And yes, it does not like an empty string. Now you have a shot at finding the bug in your code, Console.Read() required you to press the Enter key to complete but only returns a single character. The Enter key is still unprocessed, you'll get it on the next read call. Kaboom.

Get ahead by using Console.ReadKey() instead. And use int.TryParse() so a simple typing mistake does not crash your program.

Getting "Input string was not in a correct format." on SECOND step thru loop

2 Answers2