Error handling of operation calculations with C#

Question

I want to create a console calculator in C#. The data is read from a file called expressions.txt. The columns of the file consist of two numbers and an operation. I want to calculate using only the operation symbols in the file, with numbers of my choice. If I give the input a stop, it stops iterating and then exits the program. I would also like to do error handling. For example: if there is no operator in the list, I want to get a "wrong operator" message. If I want to divide by 0, or if I enter a string instead of a number, I want to get "other error" messages. I did something wrong in error handling. I would like to ask for help in correct error handling. Here is my code:

---

class Program
{

    // 1.Reading:
    static List<Expression> expressions = new List<Expression>();

    static void Read()
    {
        string[] rows = File.ReadAllLines("expressions.txt");
        foreach (var item in rows)
        {
            expressions.Add(new Expression(item));
        }

    }


    //counting:
    static void Calculator()
    {
        //string[] operators = { "div", "mod", "%", "/", "*", "-", "+" };
        string counting = "";
        string actionRequest = "";
        while (actionRequest != "stop")
        {
            Console.Write("\nI need an action:");
            actionRequest = Console.ReadLine();
            if (actionRequest != "stop")
            {
                string[] data = actionRequest.Split(' ');
                int firstNumber = int.Parse(data[0]);
                string symbol = Convert.ToString(data[1]);
                int secondNumber = int.Parse(data[2]);

                try
                {
                    counting = firstNumber + " " + symbol + " " + secondNumber;
                    switch (symbol)
                    {
                        case "mod":
                            actionRequest = counting + " = " + (firstNumber % secondNumber);
                            Console.WriteLine($"{counting} = {firstNumber % secondNumber}");
                            break;
                        case "div":
                            actionRequest = counting + " = " + (firstNumber / secondNumber);
                            Console.WriteLine($"{counting} = {firstNumber / secondNumber}");
                            break;
                        case "/":
                            actionRequest = counting + " = " + (Double.Parse(data[0]) / Double.Parse(data[2]));
                            Console.WriteLine($"{counting} = {Double.Parse(data[0]) / Double.Parse(data[2])}");
                            break;
                        case "*":
                            actionRequest = counting + " = " + (firstNumber * secondNumber);
                            Console.WriteLine($"{counting} = {firstNumber * secondNumber}");
                            break;
                        case "+":
                            actionRequest = counting + " = " + (firstNumber + secondNumber);
                            Console.WriteLine($"{counting} = {firstNumber + secondNumber}");
                            break;
                        case "-":
                            actionRequest = counting + " = " + (firstNumber - secondNumber);
                            Console.WriteLine($"{counting} = {firstNumber - secondNumber}");
                            break;
                        //default:          // --> that's the fault.
                        //    return ($"Bad operator!");
                    }
                }

                catch (Exception)
                {
                    Console.WriteLine($"Other error!");
                }



            }
            else
            {
                Console.Write("Exit ---> |press any key|");
                break;

            }



        }

    }

    static void Main(string[] args)
    {
        Read();
        Calculator();
        Console.ReadKey();
    }

}

Expression.cs:

class Expression
{

    public int op1, op2;
    public string operation;

    // ctor
    public Expression(string row)
    {
        op1 = Convert.ToInt32(row.Split()[0]);
        operation = row.Split()[1];
        op2 = Convert.ToInt32(row.Split()[2]);
    }

}

Here is the expressions.txt for the exercise:

Answer 1

Let's extract model (all possible operations) first:

static Dictionary<string, Func<double, double, double>> s_Operations = new
  Dictionary<string, Func<double, double, double>>(StringComparer.OrdinalIgnoreCase) {
    {"+",   (a, b) => a + b},
    {"-",   (a, b) => a - b},
    {"*",   (a, b) => a * b},
    {"/",   (a, b) => a / b},
    {"%",   (a, b) => a % b},
    {"div", (a, b) => a / b - a % b}, // integer division
    {"mod", (a, b) => a % b},  
    // Add more operations if required, e.g. "pow"      
  };

Keep on extracting: we are ready to implement Compute:

   static string Compute(string line) {
     if (line == null)
       return "null";

     // The simplest; spaces are mandatory: 
     // "3 + 4" is valid, when "3 +4", "3+ 4", "3+4" are not
     string[] items = line.Split(' ', StringSplitOptions.RemoveEmptyEntries);

     // if we have exactly three items: double, func, double
     // we can compute the formula
     if (items.Length == 3 &&
         double.TryParse(items[0], out var a) &&
         s_Operations.TryGetValue(items[1], out var func) &&
         double.TryParse(items[2], out var b)) 
       return $"{string.Join(" ", items)} = {func(a, b)}";
     else
       return "Syntax error";
   }  

Then we can easily process the file...

   static void Calulator() {
     foreach (var line in File.ReadLines(@"c:\myFile.txt")) {
       if (line.Trim() == "stop")
         break;

       Console.WriteLine(Compute(line));    
     }
   }

Note, that the only possible errors in this case ane number / 0 which is either +Inf or -Inf and 0 / 0 which is NaN (Not a Number).

... or implement console input:

   static void Calulator() {
     while (true) {
       Console.Write("\nI need an action:");

       string actionRequest = Console.ReadLine().Trim();

       if (actionRequest == "stop")
         break;

       Console.WriteLine(Compute(actionRequest));    
     }
   }