Input string was not in the correct format : Unhandled exception

Question

I want to calculate sum of five textboxes in 1 text box.... But when ever I remain empty one text box out of five textboxes it is giving an error Input string was not in the correct format below is my code

        if (textBox6.Text.Length == 0)

        // textBox12.Text = (Convert.ToInt32(textBox5.Text) - Convert.ToInt32(textBox11.Text)).ToString();
        {
            textBox11.Text = (Convert.ToInt32(textBox7.Text) + Convert.ToInt32(textBox8.Text) + Convert.ToInt32(textBox9.Text) + Convert.ToInt32(textBox10.Text)).ToString();
            textBox12.Text = (Convert.ToInt32(textBox5.Text) - Convert.ToInt32(textBox11.Text)).ToString();
        }
        else if (textBox7.Text.Length == 0)
        {
            //textBox11.Text = (Convert.ToInt32(textBox6.Text) + Convert.ToInt32(textBox7.Text) + Convert.ToInt32(textBox8.Text) + Convert.ToInt32(textBox9.Text) + Convert.ToInt32(textBox10.Text)).ToString();
            textBox11.Text = (Convert.ToInt32(textBox6.Text) + Convert.ToInt32(textBox8.Text) + Convert.ToInt32(textBox9.Text) + Convert.ToInt32(textBox10.Text)).ToString();
            textBox12.Text = (Convert.ToInt32(textBox5.Text) - Convert.ToInt32(textBox11.Text)).ToString();
        }
        else if (textBox8.Text.Length == 0)
        {
            //textBox11.Text = (Convert.ToInt32(textBox6.Text) + Convert.ToInt32(textBox7.Text) + Convert.ToInt32(textBox8.Text) + Convert.ToInt32(textBox9.Text) + Convert.ToInt32(textBox10.Text)).ToString();
            textBox11.Text = (Convert.ToInt32(textBox6.Text) + Convert.ToInt32(textBox7.Text) + Convert.ToInt32(textBox9.Text) + Convert.ToInt32(textBox10.Text)).ToString();
            textBox12.Text = (Convert.ToInt32(textBox5.Text) - Convert.ToInt32(textBox11.Text)).ToString();
        }
        else if (textBox9.Text.Length == 0)
        {
            //textBox11.Text = (Convert.ToInt32(textBox6.Text) + Convert.ToInt32(textBox7.Text) + Convert.ToInt32(textBox8.Text) + Convert.ToInt32(textBox9.Text) + Convert.ToInt32(textBox10.Text)).ToString();
            textBox11.Text = (Convert.ToInt32(textBox6.Text) + Convert.ToInt32(textBox7.Text) + Convert.ToInt32(textBox8.Text) + Convert.ToInt32(textBox10.Text)).ToString();
            textBox12.Text = (Convert.ToInt32(textBox5.Text) - Convert.ToInt32(textBox11.Text)).ToString();
        }
        else if (textBox10.Text.Length == 0)
        {
            //textBox11.Text = (Convert.ToInt32(textBox6.Text) + Convert.ToInt32(textBox7.Text) + Convert.ToInt32(textBox8.Text) + Convert.ToInt32(textBox9.Text) + Convert.ToInt32(textBox10.Text)).ToString();
            textBox11.Text = (Convert.ToInt32(textBox6.Text) + Convert.ToInt32(textBox7.Text) + Convert.ToInt32(textBox8.Text) + Convert.ToInt32(textBox9.Text)).ToString();
            textBox12.Text = (Convert.ToInt32(textBox5.Text) - Convert.ToInt32(textBox11.Text)).ToString();

        }
        else
            textBox11.Text = (Convert.ToInt32(textBox6.Text) + Convert.ToInt32(textBox7.Text) + Convert.ToInt32(textBox8.Text) + Convert.ToInt32(textBox9.Text) + Convert.ToInt32(textBox10.Text)).ToString();
            textBox12.Text = (Convert.ToInt32(textBox5.Text) - Convert.ToInt32(textBox11.Text)).ToString();



       // (Convert.ToInt32(textBox6.Text) +
    }

Answer 1

your code is going to get extremely messy as it goes.. I recommend you refactor..

List<string> texts = new List<string>{textbox1.Text, textbox2.Text};

int sum = 0;
foreach(string t in texts)
{
    int parse = 0;
    if(!int.TryParse(t, out parse))
        //Not a valid number
    sum += parse;   
}
textbox11.Text = sum.ToString();

You could modify this to be from a list of textboxes if you wish to tell the user which textbox is empty

---

If you are adding every textbox on the page you can just replace the list with

var texts = this.Controls.OfType<TextBox>().Select(tb => tb.Text);