Operator '-' cannot be applied to operands of type 'double' and 'string' : <p>I am asking this question because I have minimal understanding of the c sharp language and the Object-oriented paradigm. The following program was created, based on a few youtube videos and programming articles, from stack-overflow and various other sources.</p>

<pre><code> case "-":
                textBox.Text = (valor - Double.Parse(textBox.Text).ToString());
                break;
            case "*":
                textBox.Text = (valor * Double.Parse(textBox.Text).ToString());
                break;
            case "/":
                textBox.Text = (valor / Double.Parse(textBox.Text).ToString());
</code></pre>

<p>The following code segment is giving me the following errors 
    Operator '-' cannot be applied to operands of type 'double' and 'string'
for the 3 cases</p>

<p>Thank you 
Any sort of help and advice is more than welcome    </p>
