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Conversion problem

Posted on 2011-02-25
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Last Modified: 2012-05-11
Hi,
I converted this code from VB to C# but it's still not working ... getting the following error: The name 'IsNumeric' does not exist in the current context
How I can make it to work in C#. Please advise. Thanks!

if ((IsNumeric(txtTax.Text) == false)) {
        txtTax.Text = 0;
    }
    else if ((txtTax.Text == "")) {
        txtTax.Text = 0;
    }
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Question by:avi7
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11 Comments
 
LVL 16

Expert Comment

by:sjklein42
ID: 34985078
I believe this was asked earlier today (?) but here's the low-down:

There is no IsNumreric in C#.

Here is a very good discussion of what you can do instead.

It involves using try/catch blocks:

http://www.codeproject.com/KB/cs/csharp-isnumeric.aspx
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LVL 16

Assisted Solution

by:sjklein42
sjklein42 earned 100 total points
ID: 34985090
There is also a way that is described in the reference above that allows you to call the VisualBasic IsNumeric function from C# with a "using" statement.  Try this first since it may be the easiest solution.

using Microsoft.VisualBasic;

...


if ((Information.IsNumeric(txtTax.Text) == false)) {
        txtTax.Text = 0;
    }
    else if ((txtTax.Text == "")) {
        txtTax.Text = 0;
    }

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LVL 3

Expert Comment

by:sergiobg57
ID: 34985107
Use it this way:
for (int i = 0; i < textBox1.Text.Length; i++)
                if (!char.IsNumber(textBox1.Text, i))
                    MessageBox.Show("Not Number");

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Expert Comment

by:sjklein42
ID: 34985124
sergiobg57, Does that handle numbers with minus signs and decimal points?
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LVL 3

Expert Comment

by:sergiobg57
ID: 34985156
No, it doesn't, but it's adaptable for that purpose as well.
for (int i = 0; i < textBox1.Text.Length; i++)
                if (!char.IsNumber(textBox1.Text, i) && textBox1.Text[i] != '.' && textBox1.Text[i] != '-')
                {
                    MessageBox.Show("Not a Number");
                    break;
                }

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LVL 16

Expert Comment

by:sjklein42
ID: 34985224
It may not matter, but sergiobg57's test isn't the same as IsNumeric.

IsNumeric checks for a valid number, with a single decimal point (if any), and check that the minus sign is the first character, if present.  I also think it enforces at least one digit before the decimal point but am not sure about that.
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Expert Comment

by:sergiobg57
ID: 34985234
Yeah, i see.
But as i said, everything is adaptable.
C# is a great language and you'll have freedom to do whatever is needed in fact.

Having the logic, you can recreate the same effects IsNumeric has.
But for his code, i believe it would be too much.

Any way, just for fun and profit...
bool Decimal = false;
            for (int i = 0; i < textBox1.Text.Length; i++)
                if (!char.IsNumber(textBox1.Text, i))
                {
                    if((0 != i && '-' == textBox1.Text[i]) ||
                        ('.' == textBox1.Text[i] && Decimal))
                    {
                        MessageBox.Show("Not Number");
                        break;
                    }
                    
                    
                    if ('.' == textBox1.Text[i] && !Decimal)
                        Decimal = true;
                }

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LVL 16

Expert Comment

by:sjklein42
ID: 34985262
sergiobg57,  Looks good.  A useful piece of code, and more straightforward to use than cross-calling to the VB runtime.
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LVL 3

Expert Comment

by:sergiobg57
ID: 34985278
In fact, it was wrong.
During the night i'm not a good programmer.

Any way, a more readable code and free of bugs.


bool Decimal = false, NaN = false;
            for (int i = 0; i < textBox1.Text.Length; i++)
                if (!char.IsNumber(textBox1.Text, i))
                {
                    //only accepts minus as the first char
                    if ('-' == textBox1.Text[i] && i != 0)
                        NaN = true;
                    
                    //decimal points cannot be duplicated
                    if('.' == textBox1.Text[i] && Decimal)
                        NaN = true;
                    
                    //assure decimal point isn't duplicated
                    if ('.' == textBox1.Text[i] && !Decimal)
                        Decimal = true;


                    //if its not a number
                    if (NaN)
                    {
                        MessageBox.Show("Not a Number");
                        break;
                    }
                }

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Author Comment

by:avi7
ID: 34985541
Thanks!

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LVL 3

Accepted Solution

by:
sergiobg57 earned 400 total points
ID: 34985550
Last comment.
I've added it to a function(IsNumeric) and now it makes his code work.

 
public bool IsNumeric(String text)
        {
            bool Decimal = false, NaN = true;
            for (int i = 0; i < text.Length; NaN = true, i++)
                if (!char.IsNumber(text, i))
                {
                    //only accepts minus as the first char
                    if ('-' == text[i] && 0 == i)
                        NaN = false;

                    //decimal points cannot be duplicated
                    if ('.' == text[i] && !Decimal)
                        NaN = false;

                    //assure decimal point isn't duplicated
                    if ('.' == text[i] && !Decimal)
                        Decimal = true;


                    //if its not a number
                    if (NaN)
                    {
                        return false;
                    }
                }
            return true;
        }

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In his code:
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