title: How to multiply data of two columns for third column in datagridview
body: <p>I want to multiply the data of two columns and show it in the third column.</p>
  
  <p>For example:</p>
  
  <pre><code>1st Column: Quantity
  2nd Column: Rate
  3rd Column: Price
  </code></pre>
  
  <p>I want to multiply as user enters the data for quantity and rate like <code>Quantity=2</code>, <code>rate=50</code>automatically in price column I want <code>100</code> to be appear.</p>
  
  <p>Simultaneously I want to division as user enters the data for quantity and rate like <code>Price=100</code>, <code>rate=50</code>automatically in Quantity column I want <code>2</code> to be appear.</p>
  
  <p>And
   when a user enters the data for quantity and rate like <code>Price=100</code>, <code>Quantity=2</code>automatically in Rate column I want <code>50</code> to be appear.</p>
  
  <p>This three will happen in a same datagridview. User only enter any two field within this three and third will come automatically.</p>
  
  <p>Using C#, VS2008, SQL 2008</p>
  
  <pre><code>private void dataGridView2_CellEndEdit(object sender, DataGridViewCellEventArgs e) 
  { 
      int quantity,rate; 
      for (int i = 0; i &lt; dataGridView2.Rows.Count; i++) 
      { 
          if(int.TryParse(dataGridView2.Rows[i].Cells[1].Value.ToString(), out quantity) &amp;&amp; int.TryParse(dataGridView2.Rows[i].Cells[2].Value.ToString(), out rate)) 
          { 
               int price = quantity * rate; dataGridView2.Rows[i].Cells[3].Value = price.ToString(); 
          } 
      } 
  }
  </code></pre>
  
  <p>I write this code. There shows a error. Object reference not set to an instance of an object on </p>
  
  <pre><code>if(int.TryParse(dataGridView2.Rows[i].Cells[1].Value.ToString(), out quantity) &amp;&amp; int.TryParse(dataGridView2.Rows[i].Cells[2].Value.ToString(), out rate)) 
  </code></pre>
  
  <p>this line.</p>
  
  <hr>
  
  <p><img src="https://i.stack.imgur.com/6lZZy.jpg" alt="enter image description here"></p>
  
  <p>I want to do like this. User can fill any 2 field among this 3. And third will take automatically. </p>