Trouble with generic method

Question

so I've been assigned a cinema project to complete for college, which involves me taking input of type Int and DateTime. I decided to create a method to speed up the error handling for every single variable that requires checking.

static T CheckInput <T> (string message, string errorMessage, T lowerBound, T higherBound)
        {
            T input;
            do
            {
                Console.Write(message);
                try
                {
                    input = (T)Convert.ChangeType(Console.ReadLine(), typeof(T));
                }
                catch
                {
                    input = lowerBound;
                }
                if (input > higherBound || input < lowerBound) Console.Write(errorMessage);
            } while (input > higherBound || input < lowerBound);
            return input;
        }

This should technically allow me to take input of type int and Datetime, which is all I need it to do. However upon running it, the code keeps running until the datetime is valid andthen just continues the while loop without printing the user's ticket.

while (true)
{
     // Print List of films
     Console.Write("Welcome to Aquinas Multiplex\nWe are currently showing:\n");
     for (int i = 0; i < films.Length; i++)
     {
           Console.Write("{0}. {1} ({2})\n", i + 1, films[i], filmAges[i]);
     }

     // Error checking for film and age input
     filmToSee = CheckInput<int>("Please enter the number of the film you want to see: ", "That is not a valid film\n", 1, films.Length);
     age = CheckInput<int>("Please enter your age: "," Not a valid age!\n", 1, 101);

     // Age check
     if (age < filmAges[filmToSee - 1])
     {
           Console.Write("ACCES DENIED - TOO YOUNG!\n(Press any key to proceed back to homepage)");
           Console.ReadKey();
           Console.Clear();
           continue;
     }

     bookDate = CheckInput<DateTime>("Please enter the date you wish to see the film (must be no longer than a week in advance): ", "Not a valid date!\n",DateTime.Now.Date, DateTime.Now.Date.AddDays(7));

                
     Console.Clear();
     Console.Write("Your ticket:\n\n--------------------\nAquinas Multiplex\nFilm : {0}\nDate : {1}\n\nEnjoy the film!\n--------------------\n\n(Press any key to go back to the main menu)", films[filmToSee-1], bookDate.Date);
     Console.ReadKey();
     Console.Clear();
}

What is wrong with the code? I don't see anything in the while loop that would stop the final few lines and I have tried multiple ways to get the generic to output correctly. (Inputting an int to it works as intended, it's just not working for DateTime).

Answer 1

Go back to basics and add Exception handling. Wrap in try catch blocks and write the exception to console. It is important to always apply best practices. Also remember to leverage off the debugger built into your IDE and step through your code to see what it does, and what exceptions are thrown.

You will get a compilation error here:

 if (input > higherBound || input < lowerBound) Console.Write(errorMessage);

So, I am not sure how this is running? You cannot compare greatness between T and T they are constrained to type IComparable<T> . Then you can use T.CompareTo(T) . Refer to the where (generic type constraint) .