using if-else statement on combobox to choose mathematical operations (C# arithmetical operations)

Question

private void answer_Click(object sender, EventArgs e)
    {
        int textbox1;
        int textbox2;
        int answer;

        textbox1 = int.Parse(textBox1.Text);
        textbox2 = int.Parse(textBox2.Text);



        if (comboBox1.SelectedText.ToString() == "+")
        {
            answer = (textbox1 + textbox2);

        }
        else if (comboBox1.SelectedText.ToString() == "-")
        {
            answer = (textbox1 - textbox2);

        }
        else if (comboBox1.SelectedText.ToString() == "*")
        {
            answer = (textbox1 * textbox2);

        }
        else if (comboBox1.SelectedText.ToString() == "/")
        {
            answer = (textbox1 / textbox2);

        }

        // the error is here that says Use of unassigned local variable 'answer'

        MessageBox.Show(answer.ToString());

    }

• I don't understand why there's an error as i've declared the variable "answer" on the current class.
• How can i display the calculations on the messagebox for an example :

the user input 12 on textbox1 and 2 on textbox2, so they choose '-' as their operations and then the messagebox should just display 10.

Answer 1

I agree that you have to initialize the variable answer but there is another fix!

You have to use comboBox1.SelectedItem.ToString() instead of comboBox1.SelectedText.ToString()

;) Bye

Answer 2

Just assign your variable to a value when you defining it:

 int answer = 0;

If any of your conditions doesn't match then answer still will be unassigned.Compiler see this and warning you.

And your another mistake is, you are parsing textBox1.Text and textBox2.Text to integer, but you are not using that variables in your calculations.Change textboxone to textbox1 and textboxtwo to textbox2

Answer 3

Quick reformat for you:

private void answer_Click(object sender, EventArgs e)
{
    int 
        textbox1 = int.Parse(textBox1.Text), 
        textbox2 = int.Parse(textBox2.Text), 
        answer = 0;

    if (comboBox1.Text == "+")
        answer = (textbox1 + textbox2);
    else if (comboBox1.Text == "-")
        answer = (textbox1 - textbox2);
    else if (comboBox1.Text == "*")
        answer = (textbox1 * textbox2);
    else if (comboBox1.Text == "/")
        answer = (textbox1 / textbox2);

    MessageBox.Show(answer.ToString());
}

Hope you can see what was wrong with the original one.

Couple of observations:

• Be careful naming local variables with similar names like variables in outer scope ie. "textbox1" etc. all that is needed is changing the casing of "textbox1" to "textBox1" and you get a compilation error.
• Avoid comparing strings with equality operator, use string.Equals instead
• Avoid parsing int without appropriate try/catch or simply use int.TryParse (recommended)
• Avoid branching program flow by comparing string values against constants (if you can avoid it of course), in this case you can use for example ComboBox.SelectedIndex to determine which operation the user wants
• Avoid ToString-ing variables with implicit culture, you can get into trouble with formatting, in most cases for numerical values you can just use invariant culture ie. MessageBox.Show(answer.ToString(CultureInfo.InvariantCulture));