C# system.formatexception: 'input string was not in a correct format.'

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I am getting error c# system.FormatException: 'Input string was not in a correct format.' for the below code. I have tried several threads with similar heading still could not find a solution. Please help.

What I have tried:

private void txtDiscount_TextChanged(object sender, EventArgs e)
        {
            // Calculate Discount and Final Fee
            double FinalFee;
            double CourseFee1;
            double Disc;
            CourseFee1 = Convert.ToDouble(lblCourseFee.Text);
            Disc = Convert.ToDouble(txtDiscount.Text);
            FinalFee = CourseFee1 - (CourseFee1 * (Disc / 100));            

            if (Disc > 40)
            {
                string message = "Maximum Discount is 40% ";
                string title = "Discount Maximum Limit Exceeded";
                MessageBoxButtons buttons = MessageBoxButtons.OK;
                DialogResult result = MessageBox.Show(message, title, buttons, MessageBoxIcon.Warning);
            }
            else
            {
                lblFinalFee.Text = FinalFee.ToString("N2");
            }
        }

Posted 12-Feb-22 21:17pm

Premasara Sampath Illankoon

Updated 13-Feb-22 4:04am

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Richard MacCutchan 13-Feb-22 3:22am

Which line causes the error, and what data is it trying to convert?

3 solutions

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OriginalGriff · Accepted Answer · 2022-02-12T21:38:00

Never use Convert methods with user input: they throw an exception if the user mistypes.
Instead, use the double.TryParse method which returns an error:

double courseFee;
if (!double.TryParse(lblCourseFee.Text, out courseFee))
   {
   ... report problem to user ...
   return;
   }
double disc;
if (!double.TryParse(txtDiscount.Text, out disc))
   {
   ... report problem to user ...
   return;
   }
double finalFee = courseFee - courseFee * disc / 100.0;

M Imran Ansari · Accepted Answer · 2022-02-12T22:17:00

Error is on line

C#

Disc = Convert.ToDouble(txtDiscount.Text); 
OR CourseFee1 = Convert.ToDouble(lblCourseFee.Text);

because you are converting value into double. Verify you are giving the correct numeric value. There ould be a change a character or any other character coming into this filed which cause an error.

Premasara Sampath Illankoon · Accepted Answer · 2022-02-13T04:04:00

Solution 4

Thanks everyone for your valuable inputs.
I solved the issue with below code.

bool valid1 = float.TryParse(lblCourseFee.Text, out CourseFee);

bool valid2 = float.TryParse(txtDiscount.Text, out Disc);

Found it on another website. Serves the purpose.
Thanks again.

Posted 13-Feb-22 4:04am

Premasara Sampath Illankoon

Comments

M Imran Ansari 13-Feb-22 13:14pm

Great. Happy Coding!!

Richard Deeming 14-Feb-22 10:51am

If your variables are declared as double, why are you using float.TryParse instead of double.TryParse? That will give you a compiler error:

CS1503 Argument 2: cannot convert from 'out double' to 'out float'

C# system.formatexception: 'input string was not in a correct format.'

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