C# How to use a textbox variable

Shane Nicholson

Good day everyone,

First of all, thank you for taking the time to read my request, it means alot.

I have created a windows form on VB 2019.

When a user puts a number into textbox 5, I want the following equation to be calculated and the total displayed in Textbox8.

The below works to some level, but if the number is negative (example: -200) it does not work.

Also if the user tries to clear the text box, it always crashes with the same error " System.FormatException: 'Input string was not in a correct format.'

My guess is this has something to do with the variable I am using and cannot recognise a character.

Thanks again people, I really appreciate your time and expertise.

private void textBox5_TextChanged(object sender, EventArgs e)
{
double firstbox;
double answer;
firstbox = double.Parse(textBox5.Text);
answer = firstbox / 1000 * 3.18141 * 2.3 * 1.19;
textBox8.Text = (answer.ToString());
}

2 Replies

Know the answer? Post it — somebody with the same question will find it here.

Amit Mohanty5y ago
Accepted answer
Hey, try this
if (!string.IsNullOrEmpty(textBox5.Text) && textBox5.Text != "-")
{
    double firstbox;
    double answer;
    var format = new NumberFormatInfo(); //For NumberFormatInfo() use using System.Globalization;
    format.NegativeSign = "-";
    format.NumberDecimalSeparator = ".";

    firstbox = double.Parse(textBox5.Text, format);
    answer = firstbox / 1000 * 3.18141 * 2.3 * 1.19;
    textBox8.Text = (answer.ToString());
}
Shane Nicholson5y ago
Hey Amit,

You are brilliant. Thank you so much for taking the time to reply.
I need to spend some time understanding what you did now :)

Best regards Amit.