title: how to display the result in textbox of a row in datagridview?
body: <p>I want to create a small program to create an arithmetic operator that adds two numbers together.</p>
  
  <p>when I double click a cell in my datagridview, then my textbox outside will display the result of this row.</p>
  
  <p>for example:</p>
  
  <pre><code>1  3
  3  5
  2  8
  </code></pre>
  
  <p>I also create a class for my program, the class's name is Cac, and the method in it is </p>
  
  <pre><code>public int CacAB()
      {
          int result= a + b;
          return result;
      }
  </code></pre>
  
  <p>the result for first row should be 4, second row should be 8 and the third row should be 10.</p>
  
  <p>my textbox's name is just textBox1 and my datagridview's name is just datagridview1, how to make it? thanks very much.</p>
  
  <p>I know I need create a method like:"dataGridView1_CellDoubleClick" so far.</p>