/// <summary>
/// Method used to display the result of a valid mathematical expression in reverse polish notaion.
/// </summary>
/// <param name="userInput">To be evaluated as a boolean decision.</param>
/// <returns>Boolean representing user's decision to continue or exit the program.</returns>
public static bool DisplayResult(ref ReversePolishExpressionBuilder expressionBuilder, string userInput)
{
// Validate, build, and evaluate an expression from user input to be stored in the expressionBuilder.
expressionBuilder.ExpressionString = userInput;
// Display result and prompt for user to continue calculating other expressions or exiting.
bool first = true;
while (true)
{
if (first)
{
Console.WriteLine($" Result: {expressionBuilder.Result}");
} // Only show result once.
Console.Write("\n Evaluate another reverse polish expression? (y/n)"); // Can repeatedly display.
Console.CursorLeft = 53; // Adjust cursor position.
string userDecision = Console.ReadKey().KeyChar.ToString(); // Detect user keystroke.
switch (userDecision.ToLower()) // Ensuring userDecision filtered to detect capital letters.
{
case "y": // Return to prompt user for another expression (main prompt).
return(true);
case "n":
return(false); // Return to exit the program.
default:
Console.ForegroundColor = ConsoleColor.Red;
Console.Write("\n INVALID KEYSTROKE; TRY AGAIN.\n");
Console.ForegroundColor = ConsoleColor.White;
first = false; // Prompt user for another decision when keystroke is invalid.
break;
}
}
}
/// <summary>
/// Main method for this console program allows users to input mathematical expressions in reverse polish
/// (postfix) notation with integer constants, acceptable operators {+, -, *, /, ^}, and whitespace. This program
/// has a feature using some additional logic here, which allows user inputs with whitespace ignored around operators.
/// </summary>
/// <param name="args">Not used.</param>
public static void Main(string[] args)
{
// Create a expression visitor/builder to be passed by reference.
ReversePolishExpressionBuilder expressionBuilder = new ReversePolishExpressionBuilder();
Console.WindowWidth = 79;
bool running = true; // Flag used to remain in loop displaying options.
string userInput; // Declaring the user input to be read from console.
// Loop until user enters 'exit' in expression prompt or chooses option 'n' to finish evaluating expressions.
while (running)
{
try
{
Console.Clear();
userInput = PromptForExpression(); // Get user input.
// Condition to either exit program or DisplayResult with prompt - following PromptForExpression.
if (userInput.ToLower().Equals("exit") || !DisplayResult(ref expressionBuilder, userInput))
{
running = false;
Console.Clear();
Console.ForegroundColor = ConsoleColor.DarkCyan;
Console.WriteLine("\n\tEXITING REVERSE POLISH CALCULATOR... GOODBYE!\n");
Console.ResetColor();
}
}
catch (FormatException ex) // Thrown when attempted expression build has invalid characters or formatting.
{
Console.Clear();
Console.Beep();
Console.WriteLine($"\n\tError: {ex.Message}");
expressionBuilder.Reset(); // Resets the builder after an error to accept other user input.
Console.ForegroundColor = ConsoleColor.Red;
Console.WriteLine("\n\t" +
"\n\n\tMUST INPUT VALID EXPRESSION IN REVERSE POLISH NOTATION!" +
"\n\n\tPRESS ANY KEY TO CONTINUE...");
Console.ResetColor();
Console.ReadKey();
}
catch (ArgumentOutOfRangeException ex) // Thrown whenever provided an integer too large.
{
Console.Clear();
Console.Beep();
Console.WriteLine($"\n\tError: {ex.Message}");
expressionBuilder.Reset(); // Resets the builder after an error to accept other user input.
Console.ForegroundColor = ConsoleColor.Red;
Console.WriteLine("\n\t" +
"\n\n\tMUST INPUT VALID EXPRESSION WITH INTEGERS FROM -2,147,438,648 TO 2,147,483,647" +
"\n\n\tPRESS ANY KEY TO CONTINUE...");
Console.ResetColor();
Console.ReadKey();
}
}
}