title: C# Calculator Logic
body: <p>when I press 9 and then press times the display shows 9 and when I press 9 again it'll add it to the first number (9) instead of clearing the first 9. so it thinks its 9*99. how do I clear the display on the first input after an operation? </p>
  
  <pre><code>using System;
  using System.Collections.Generic;
  using System.ComponentModel;
  using System.Data;
  using System.Drawing;
  using System.Linq;
  using System.Text;
  using System.Threading.Tasks;
  using System.Windows.Forms;
  
  namespace WindowsFormsApplication2
  {
  
      public partial class Form1 : Form
      {
          string input = string.Empty;
          string operand1 = string.Empty;
          string operand2 = string.Empty;
          char operation;
          double result = 0.0;
  
          public Form1()
          {
              InitializeComponent();
          }
  
          private void Multiply_Click(object sender, EventArgs e)
          {
              operation = '*';
              if (operand1 != "")
              {
                  calculate();
              }
              else
              {
                  operand1 = input;
              }
          }
  
          private void Minus_Click(object sender, EventArgs e)
          {
              operation = '-';
              if (operand1 != "")
              {
                  calculate();
              }
              else
              {
                  operand1 = input;
              }
          }
  
          private void Addition_Click(object sender, EventArgs e)
          {
              operation = '+';
              if (operand1 != "")
              {
                  calculate();
              }
              else
              {
                  operand1 = input;
              }
          }
  
          private void Divide_Click(object sender, EventArgs e)
          {
              operation = '/';
              if (operand1 != "")
              {
                  calculate();
              }
              else
              {
                  operand1 = input;
              }
          }
  
          private void textBox1_TextChanged(object sender, EventArgs e)
          {
  
          }
  
          private void five_Click(object sender, EventArgs e)
          {
              this.textBox1.Text = "";
              input += "5";
              this.textBox1.Text += input;
          }
  
          private void Zero_Click(object sender, EventArgs e)
          {
              this.textBox1.Text = "";
              input += "0";
              this.textBox1.Text += input;
          }
  
          private void one_Click(object sender, EventArgs e)
          {
              this.textBox1.Text = "";
              input += "1";
              this.textBox1.Text += input;
          }
  
          private void two_Click(object sender, EventArgs e)
          {
              this.textBox1.Text = "";
              input += "2";
              this.textBox1.Text += input;
          }
  
          private void three_Click(object sender, EventArgs e)
          {
              this.textBox1.Text = "";
              input += "3";
              this.textBox1.Text += input;
          }
  
          private void four_Click(object sender, EventArgs e)
          {
              this.textBox1.Text = "";
              input += "4";
              this.textBox1.Text += input;
          }
  
          private void six_Click(object sender, EventArgs e)
          {
              this.textBox1.Text = "";
              input += "6";
              this.textBox1.Text += input;
          }
  
          private void seven_Click(object sender, EventArgs e)
          {
              this.textBox1.Text = "";
              input += "7";
              this.textBox1.Text += input;
          }
  
          private void eight_Click(object sender, EventArgs e)
          {
              this.textBox1.Text = "";
              input += "8";
              this.textBox1.Text += input;
          }
  
          private void nine_Click(object sender, EventArgs e)
          {
              this.textBox1.Text = "";
              input += "9";
              this.textBox1.Text += input;
          }
  
          private void Equal_Click(object sender, EventArgs e)
          {
              calculate(); 
          }
  
          private void Decimal_Click(object sender, EventArgs e)
          {
              this.textBox1.Text = "";
              input += ".";
              this.textBox1.Text += input;
          }
  
          private void Clear_Click(object sender, EventArgs e)
          {
              textBox1.Clear();
          }
  
          public void calculate()
          {
              Console.WriteLine("performing operation" + operand1 + " " + operation + " " + operand2 + "= ???" + "the input is?" + input);
              operand2 = input;
              double num1, num2;
              double.TryParse(operand1, out num1);
              double.TryParse(operand2, out num2);
  
              if (operation == '*')
              {
                  result = num1 * num2;    
              }
  
              if (operation == '-')
              {
                  result = num1 * num2;
              }
  
              if (operation == '+')
              {
                  result = num1 * num2;
              }
  
              if (operation == '/')
              {
                  result = num1 * num2;
              }
              textBox1.Text = result.ToString();
              input = result.ToString();
          }
      }
  }
  </code></pre>