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Cannot implicitly convert type 'string' to 'double'

Posted on 2011-02-24
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Last Modified: 2012-05-11
Hi, I'm new to c# and am trying to convert the following code:
Thanks!

private void Sum()
    {
        double Price1 = 0;
        double Price2 = 0;

if (txtItemPrice1.Text == "")  
        {
            Price1 = 0.0;
        }
        else
        {
            Price1 = txtItemPrice1.Text; <----
        }

        if (txtItemPrice2.Text == "")
        {
            Price2 = 0.0;
        }
        else
        {    
            Price2 = txtItemPrice2.Text; <---
        }

      Error Cannot implicitly convert type 'string' to 'double'

if (IsNumeric(txtTax.Text) == false)  <----
        {
            txtTax.Text = 0.0;
        }
        else if (txtTax.Text == "")
        {
            txtTax.Text = 0.0;
        }      

TotalAmt = FormatNumber(Price1 + Price2 + txtTax.Text);      
 txtItemPriceAmt.Text = FormatNumber(TotalAmt, 2);  

Error The name 'IsNumeric' does not exist in the current context
0
Comment
Question by:avi7
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6 Comments
 
LVL 8

Expert Comment

by:crysallus
ID: 34976598
conversions in C# are normally done using the Convert class, such as

Price2 = Convert.ToDouble(txtItemPrice2.Text);

Here's the link for all the function's available:

http://msdn.microsoft.com/en-us/library/system.convert%28v=VS.100%29.aspx

To check whether a text string can be converted to a number, use the TryParse methods of one the classes representing the base data type that your number could be in. For example, if you want to test whether the text can be converted to a double, use

if (Double.TryParse(txtTax.Text, out result) == false)
...

http://msdn.microsoft.com/en-us/library/994c0zb1.aspx
0
 
LVL 16

Assisted Solution

by:Peter Kwan
Peter Kwan earned 200 total points
ID: 34976606
1) To convert a string to Double, you may use Conver.ToDouble(<your string>)
2) For checking if a string is numeric, you may use "Double.TryParse" method
http://msdn.microsoft.com/en-us/library/994c0zb1.aspx
0
 
LVL 8

Assisted Solution

by:crysallus
crysallus earned 800 total points
ID: 34976621
In fact, your first 2 if else structures could simply be rewritten as:

Double.TryParse(txtItemPrice1.Text, out Price1);
Double.TryParse(txtItemPrice2.Text, out Price2);

because if the text can't be converted to a double, then the double variable is assigned 0 anyway, so there's no need for you to check whether it's empty or not.
0
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LVL 11

Accepted Solution

by:
dougaug earned 1000 total points
ID: 34976632
Try the following code:

private void Sum()
    {
        double Price1 = 0;
        double Price2 = 0;
        double Tax;

        if (txtItemPrice1.Text == "")  
        {
            Price1 = 0.0;
        }
        else
        {
            Price1 = Double.Parse(txtItemPrice1.Text);
        }

        if (txtItemPrice2.Text == "")
        {
            Price2 = 0.0;
        }
        else
        {    
            Price2 = Double.Parse(txtItemPrice2.Text);
        }

        if (Double.TryParse(txtTax.Text, out Tax) == false)  
        {
            txtTax.Text = 0.0;
        }

TotalAmt = FormatNumber(Price1 + Price2 + txtTax.Text);      
 txtItemPriceAmt.Text = FormatNumber(TotalAmt, 2);  

0
 
LVL 8

Expert Comment

by:crysallus
ID: 34976651
TryParse doesn't throw exceptions, Parse does. If you are going to use Parse as dougang suggested, you would have to surround those calls with a try-catch block. Using TryParse avoids the need for exception handling.
0
 

Author Comment

by:avi7
ID: 34976818
Thanks!
0

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