Input string was not in the correct form

Question

a C# beginner here. I've been following a guide on making a simple calculator. Everything worked fine 'till I added the point button. If I use the calculator to calculate basic integers there's no problem. However, when I add in the point button to calculate doubles with a decimal it gets all screwed up. Any ideas?

    // Above this are the numeric buttons, no problem with those

    private void btnPoint_Click(object sender, EventArgs e)
    {
        txtDisplay.Text = txtDisplay.Text + btnPoint.Text;
    }

    double total1 = 0; 
    double total2 = 0; 

    private void btnPlus_Click(object sender, EventArgs e)
    {
        total1 = total1 + double.Parse(txtDisplay.Text); // Error comes here
        txtDisplay.Clear();
    }

    private void btnEquals_Click(object sender, EventArgs e)
    {
        total2 = total1 + double.Parse(txtDisplay.Text); // And one time it came here
        txtDisplay.Text = total2.ToString(); 
        total1 = 0; 
    }

It's the text box value so it's value is user input. It calculates fine if there's no decimals but once I add in a number with decimals it gives me the error. — user2999898, Nov 16 '13 at 17:49
@user2999898: A value such as? Please give the *exact string*, as well as which culture you're in. — Jon Skeet, Nov 16 '13 at 17:49
@JonSkeet I think the sad part of this question is, there are already 3 answers even they don't know _exact string_ and OP's culture. — Soner Gönül, Nov 16 '13 at 17:52
possible duplicate of [How do I parse a string with a decimal point to a double?](http://stackoverflow.com/questions/1354924/c-how-do-i-parse-a-string-with-a-decimal-point-to-a-double) — CodeCaster, Nov 16 '13 at 17:56
@CodeCaster: Thanks for that, couldn't find that myself and it solved my issue. It was simply the fact that my computer was expecting a ',' instead of a '.'. — user2999898, Nov 16 '13 at 18:04

score 0 · Answer 1 · answered Nov 16 '13 at 18:00

Time ago I've made a simple calculator and for checking the input I have used regex(if you don't know what is a Regex take a look here

You can use this regex for checking the input: ^[0-9]{0,}([.,][0-9]{1,})?$ It allows:

But not

.1
,1
 And all type of string

For using the regex in c# you must declare a Regex object. Before that you need to add using System.Text.RegularExpressions; Than use the regex is quite simple

Regex regex=new Regex(pattern);
if(regex.IsMatch(myTextBox.Text))
{//Do something
}
else{//Catch the error
}

If you want know more about regular expression take a look here

score -1 · Answer 2 · answered Nov 16 '13 at 17:49

-1

Instead of using Double.Parse use Double.TryParse.

private void btnPlus_Click(object sender, EventArgs e)
{
    Double v = 0;
    if ( Double.TryParse(txtDisplay.Text.Trim(), out v)
    {
        total1 = total1 + v;
        txtDisplay.Clear();
    }
    else
    {
        // Invalid value
    }

}

answered Nov 16 '13 at 17:49

Muhammad Umar

3,761
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2

[`Double.TryParse()` differs from the Double.Parse(String) method by returning a Boolean value that indicates whether the parse operation succeeded instead of returning the parsed numeric value.](http://msdn.microsoft.com/en-us/library/994c0zb1(v=vs.110).aspx) This doesn't resolve OP's problem as the parsing will still fail, it just returns a boolean instead of throwing an exception. – CodeCaster Nov 16 '13 at 17:55

Input string was not in the correct form

2 Answers2