multiplying int to double c#

Question

I want to to multiply textbox1(int) by textbox2(double) and return a double in textbox3 Im doing an Invoice app and need to multiply quantity by rate to get amount so far I have this...

private void textbox2_TextChanged(object sender, system.EventArgs e)
{
 int32 qty = int32.Parse(Textbox1.text);
 Double rate = Double.Parse(Textbox2.text);
 Double amt = qty * rate;
 textbox3.text = amt.ToString();
}

Where am I going wrong?

Same question as above and also is there any reason that you could not parse them both to doubles? — Daniel Casserly, Dec 27 '12 at 09:46
One thing you might want to think about is how you handle things if the textbox doesn't contain numbers (eg somebody writes text in there). For this reason you might wnat to look at `TryParse` methods instead of plain `Parse`. — Chris, Dec 27 '12 at 09:50
@BizApps: I don't think that will make a difference to anything... — Chris, Dec 27 '12 at 09:50
I also get a runtime error that the qty input string was not in the correct format — Jose Rivas, Dec 27 '12 at 09:55
You can use Format providers http://msdn.microsoft.com/en-us/library/shxtf045.aspx — coder_bro, Dec 27 '12 at 09:56
@JoseRivas Your only error is that you are not properly validating input. The key rule is: _"input is not valid unless it's proven to be valid"_. — Leri, Dec 27 '12 at 09:56
You should not be using doubles in the first place if this is an invoice; use doubles to solve *physics* problems. Use decimal to solve financial problems; that is what it was designed for. — Eric Lippert, Dec 27 '12 at 14:51

score 4 · Accepted Answer · edited Sep 11 '18 at 05:17

4

First of all you need to check whether the first text box is not empty or blank spaces. Then if your first text box is empty or blank space then give appropriate message to user.

Try the example below:

if (!string.IsNullOrWhiteSpace(Textbox1.text))
{
    int qty = Int32.Parse(Textbox1.text);
    double rate = Double.Parse(Textbox2.text);
    Textbox3.text = (rate* (double) qty).ToString();
}
else
{
    //Give appropriate message to user for entering quantity in textbox 1
}

edited Sep 11 '18 at 05:17

ivcubr

1,988
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answered Dec 27 '12 at 09:59

Tejas Vaishnav

466
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I'm still getting 4 * 10.00 = 40 and not 40.00 – Jose Rivas Dec 27 '12 at 10:13
okay I used this but changed double to decimal and it worked – Jose Rivas Dec 27 '12 at 10:17
you can directly cast or formate your string like this... Textbox3.text = amt.ToString("0.00"); – Tejas Vaishnav Dec 27 '12 at 10:28
for this review this link... http://www.csharp-examples.net/string-format-double/ – Tejas Vaishnav Dec 27 '12 at 10:29
Casting `qty` to `double` is really not necessary. Result of `double * int` is always `double`. – Teejay Apr 19 '17 at 09:21

score 1 · Answer 2 · answered Dec 27 '12 at 09:54

1

Try this out

  textBox3.Text = (Int32.Parse(textBox1.Text) * Double.Parse(textBox2.Text)).ToString();

answered Dec 27 '12 at 09:54

Nejthe

353
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score 0 · Answer 3 · answered Dec 27 '12 at 09:50

0

First off. When you are dealing with money, always use decimal, not double. And with decimals, there is always the problem with users using both comma and dot as decimal separator.

This code worked for me:

    int qty = Int32.Parse("2");
    Decimal rate = Decimal.Parse("3.14".Replace(".", ","));
    Decimal amt = qty * rate;
    Console.WriteLine(amt);

answered Dec 27 '12 at 09:50

Michael Viktor Starberg

920
5
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2

Wouldn't that code only work for locales where the decimal seperator is a comma? – PeterJ Dec 27 '12 at 09:51
Yes. It is better to use proper culture handling if you target multiple locales. – Michael Viktor Starberg Dec 27 '12 at 10:09

multiplying int to double c#

3 Answers3