act

using System;
using System.Windows.Forms;
using CalculatorPrivateAssembly;

namespace BasicCalculator1
{
    public partial class frmBasicCalculator : Form
    {
        public frmBasicCalculator()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            if (cbOperator.SelectedItem == null)
            {
                rtbResult.Text = "Error:\n" + "Please select an Operator.";
            }
            float a = 0, b = 0;
            parseCheck(tbNum1, out a, "First");
            parseCheck(tbNum2, out b, "Second");

            if (a != 0 && b != 0 && cbOperator != null)
            {
                switch (cbOperator.SelectedItem)
                {
                    case "x":
                        printResult(BasicCalculator.Multiplication(a, b));
                        break;
                    case "/":
                        printResult(BasicCalculator.Division(a, b));
                        break;
                    case "+":
                        printResult(BasicCalculator.Addition(a, b));
                        break;
                    case "-":
                        printResult(BasicCalculator.Subtraction(a, b));
                        break;
                }
            }
        }

        void parseCheck(TextBox a, out float b, string c)
        {
            if (!float.TryParse(a.Text, out b))
            {
                rtbResult.Text = "Error:\n" + c + " entry is invalid";
            }
        }

        void printResult(float a)
        {
            rtbResult.Text = "Result:\n" + a.ToString();
        }
    }
}