Calculate percentage formula is not working

Question

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I have a form that will show what the percentage of two number. When a user enters a number say 40 and then the next number is 30, the calculation is done and the answer should be 33%. When the user enters the numbers, the answer comes to be -60. Why is this happening? What did I forget in my formula?

C#

protected void TextBox3_TextChanged(object sender, EventArgs e)
       {
           int a = Convert.ToInt32(TextBox2.Text);
           int b = Convert.ToInt32(TextBox3.Text);
           TextBox4.Text = Convert.ToString(a - b / b * 100);
       }

SQL

The percentage increase from 30 to 40 is:
  (40-30)/30 * 100 = 33%

Posted 22-Sep-14 5:08am

Computer Wiz99

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Comments

PIEBALDconsult 22-Sep-14 11:17am

:cough: Order of operations :cough:

And please don't use Convert, use Int32.TryParse instead. Better yet, use a NumericUpDown rather than a TextBox.

Computer Wiz99 22-Sep-14 11:20am

Okay. I was just testing the formula to see what I did wrong.

3 solutions

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Aarti Meswania · Accepted Answer · 2014-09-22T05:15:00

Solution 1

it is due to you have not add brackates

C#

TextBox4.Text = Convert.ToString((a - b) / (b*1.0) * 100);

Happy Coding! :)

Posted 22-Sep-14 5:15am

Aarti Meswania

Updated 22-Sep-14 5:21am

v2

Comments

Computer Wiz99 22-Sep-14 11:17am

Aarti Meswania, I have tried this and the answer came to be 0.

PIEBALDconsult 22-Sep-14 11:19am

Then step through with a debugger to see what actual values are being used.

Aarti Meswania 22-Sep-14 11:20am

values should be float

Aarti Meswania 22-Sep-14 11:22am

please check updated solution

Sergey Alexandrovich Kryukov 22-Sep-14 11:52am

5ed. I added my 2 cents in Solution 3.
—SA

Aarti Meswania 22-Sep-14 12:02pm

Thank you, Sergey Alexandrovich Kryukov
:)

pietvredeveld · Accepted Answer · 2014-09-22T05:23:00

Solution 2

Compare your'e example and code. But you should study the precedence and order of evaluation in C#
See

http://msdn.microsoft.com/en-us/library/2bxt6kc4.aspx[^]

Posted 22-Sep-14 5:23am

pietvredeveld

Comments

Computer Wiz99 22-Sep-14 11:33am

Thanks for the link. This will help out a lot.

Sergey Alexandrovich Kryukov 22-Sep-14 11:52am

5ed. I added my 2 cents in Solution 3.
—SA

Sergey Alexandrovich Kryukov · Accepted Answer · 2014-09-22T05:51:00

Solution 3

In addition to Solutions 1-2: don't use Convert, use Parse or TryParse, and ToString (possibly with format). Explicitly use double type (or float) to calculate percentage.

—SA

Posted 22-Sep-14 5:51am

Sergey Alexandrovich Kryukov

Comments

Aarti Meswania 22-Sep-14 12:02pm

5+! :)
TryParse and double type will make code perfect

Sergey Alexandrovich Kryukov 22-Sep-14 12:10pm

Thank you very much, Aarty, but "perfect" would be a great exaggeration. :-)
—SA

Aarti Meswania 22-Sep-14 12:14pm

welcome!
it isn't exaggeration. It's really perfect solution :)

Sergey Alexandrovich Kryukov 22-Sep-14 12:36pm

Do you want me to point out other problems? :-)
—SA

Sergey Alexandrovich Kryukov 22-Sep-14 12:37pm

Do you want me to point out other problems? :-)
I mean the code which would result in implementing our suggestions minimally?
—SA

Aarti Meswania 22-Sep-14 12:40pm

no didn't mean that SA :)

Sergey Alexandrovich Kryukov 22-Sep-14 12:56pm

All right then.
Thank you.
—SA

Aarti Meswania 22-Sep-14 12:59pm

:)

Calculate percentage formula is not working

3 solutions

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Solution 3

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Calculate percentage formula is not working

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