Question

I’m trying to program a calculator in which the buttons send a character to a textbox. When the user presses the “equals” button, the whole string must be calculated and the answer must be displayed as a decimal. Obviously the following doesn’t work:

    private void btn_enter_Click(object sender, EventArgs e)
    {
        decimal answer;
        answer = Convert.ToDecimal(textBox1.Text);

        textBox1.Text += "=" + answer;
    }

What is the best way to make something like this works?

Answer 1

You could go along the lines of evaluating C# on the fly, but for what you’re trying to do, it’s a bit overkill.

I’d recommend a calculation engine, like NCalc (which you can get on NuGet). With it, you can easily do something like (taken from the NCalc homepage):

Expression e = new Expression("2 + 3 * 5");
Debug.Assert(17 == e.Evaluate());

You could replace the constructor of the Expression class with the text from your TextBox and then pipe the result of the call to Evaluate to wherever you want to output it to:

Expression e = new Expression(textBox1.Text);
MessageBox.Show(e.Evaluate().ToString());