coding-horror/basic-computer-games · error · ArgumentException

{DisplayText} must be greater than zero

Error message

{DisplayText} must be greater than zero

What it means

Thrown as ArgumentException by GetNumber() in the Banner program when the parsed integer is <= 0. Int32.TryParse writes 0 into TempInt on failure (non-numeric or null input), so both genuinely non-positive input and unparseable garbage trigger it. GetNumber feeds Horizontal/Vertical scaling factors for the banner print, which must be positive.

Source

Thrown at 06_Banner/csharp/banner.cs:83

        };


        /// <summary>
        /// This displays the provided text on the screen and then waits for the user
        /// to enter a integer value greater than 0.
        /// </summary>
        /// <param name="DisplayText">Text to display on the screen asking for the input</param>
        /// <returns>The integer value entered by the user</returns>
        private int GetNumber(string DisplayText)
        {
            Console.Write(DisplayText);
            string TempStr = Console.ReadLine();

            Int32.TryParse(TempStr, out int TempInt);

            if (TempInt <= 0)
            {
                throw new ArgumentException($"{DisplayText} must be greater than zero");
            }

            return TempInt;
        }

        /// <summary>
        /// This displays the provided text on the screen and then waits for the user
        /// to enter a Y or N.  It cheats by just looking for a 'y' and returning that
        /// as true.  Anything else that the user enters is returned as false.
        /// </summary>
        /// <param name="DisplayText">Text to display on the screen asking for the input</param>
        /// <returns>Returns true or false</returns>
        private bool GetBool(string DisplayText)
        {
            Console.Write(DisplayText);
            return (Console.ReadLine().StartsWith("y", StringComparison.InvariantCultureIgnoreCase));
        }

View on GitHub (pinned to 5301155192)

Solutions

1. Enter a positive integer (1 or greater) at the Horizontal/Vertical prompts.
2. If automating, pipe a positive integer into stdin for those prompts.
3. Make GetNumber loop and re-prompt on <= 0 instead of throwing, for a friendlier UX.

Example fix

// before
Int32.TryParse(TempStr, out int TempInt);
if (TempInt <= 0) {
    throw new ArgumentException($"{DisplayText} must be greater than zero");
}
return TempInt;

// after: re-prompt instead of throwing
int TempInt;
while (!Int32.TryParse(Console.ReadLine(), out TempInt) || TempInt <= 0) {
    Console.Write($"{DisplayText} must be a positive integer. Try again: ");
}
return TempInt;

// C#: validate before relying on TryParse result
int GetNumber(string prompt) {
  int value;
  while (!Int32.TryParse(Console.ReadLine(), out value) || value <= 0) {
    Console.Write($"{prompt} must be a positive integer: ");
  }
  return value;
}

// In GetInput(), catch and re-prompt instead of letting it propagate
try { Horizontal = GetNumber("Horizontal "); }
catch (ArgumentException) { /* re-ask or default */ }

When it happens

Trigger: User pressing Enter without typing (null/empty -> TryParse fails -> TempInt=0); typing 0, a negative number, or letters like 'abc' at the 'Horizontal ' or 'Vertical ' prompts in GetInput() (banner.cs:119-120).

Common situations: Empty input at the dimension prompt; a user typing a negative dimension; pasting non-numeric text; running the program with redirected empty stdin.

AI-assisted analysis of coding-horror/basic-computer-games@5301155192 (2026-08-13). Data as JSON: /api/errors/bac2707a6523a50a. Report an issue: GitHub.