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05.11.2006 at 09:59PM PDT, ID: 21847875

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7.8

Making TextBox handle Numeric values? [Visual C++]

Zone: Microsoft Visual C++.Net

Tags: textbox, visual, numeric

Hello,

Ok, here I am asking the same question again! I was thinking it is so basic an I would have no problem finding an answer in no time. But after searching and asking for days, I got nothing!

Here is the question:

A textbox control can handle data of Text type only. For example, if I have a form with a TextBox named textBox1, and I have the following code under a button:

int x;

x = textBox1->text;

I woul get the following error when compiling:

error C2440: '=' : cannot convert from 'System::String ^' to 'int'

The same applies to reading numeric values from a textbox.

Now, how can I change the data type of a textbox to integer or float so that it can handle numirec values?

Would appreciate any input.

Thank you in advance,

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Question Stats

Zone: Programming

Question Asked By: Mahmoodaman

Solution Provided By: AlexFM

Participating Experts: 2

Solution Grade: A

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05.12.2006 at 01:44AM PDT, ID: 16665608

Rank: Master

mahesh1402:

convert string to int using function like atoi()

int x;
x = atoi(textBox1->text);

to convert to float you may use atof()

float x;
x = atof(textBox1->text);

-MAHESH

05.12.2006 at 04:31AM PDT, ID: 16666495

Rank: Wizard

AlexFM:

int x;

try
{
x = Int32::Parse(textBox1->text);
}
catch (FormatException^ e)
{
// handle error
}
catch (OverflowException ^ e)
{
// handle error
}

Take a look also at MaskedTextBox class.

05.12.2006 at 05:44AM PDT, ID: 16666976

Mahmoodaman:

Thank you for your respones MAHESH,

I am getting this error:
error C3861: 'atoi': identifier not found

Any idea what might be wrong?

05.12.2006 at 05:49AM PDT, ID: 16667023

Mahmoodaman:

Thank you for your response AlexFM,

I am gettin the following error when trying your code:

error C2248: 'System::Windows::Forms::Control::text' : cannot access private member declared in class 'System::Windows::Forms::Control

Any idea what might be wrong?

05.12.2006 at 06:07AM PDT, ID: 16667178

Rank: Wizard

AlexFM:

Should be: textBox1->Text

I just copied your code, this was mistake.

05.12.2006 at 06:09AM PDT, ID: 16667209

Rank: Wizard

AlexFM:

About atoi - you need to add appropriate include line: <stdlib.h>
But it is not good idea to use CRT functions in C++/CLI application. .NET contains all required functions and replaces CRT for managed code.

05.12.2006 at 08:26AM PDT, ID: 16668364

Mahmoodaman:

Thank you AlexFM,

I really appreciate your help.

I added #include<stdlib.h> and changed "text" to "Text". I am now getting the following error:

error C2664: 'atoi' : cannot convert parameter 1 from 'System::String ^' to 'const char *'

Would you please suggest a reason for this error?

05.12.2006 at 09:02AM PDT, ID: 16668713

Rank: Wizard

AlexFM:

Please show your code. Where did you find char* in managed application? Do you use my suggestion with Int32::Parse or atoi function?
Again: you don't need atoi and stdlib.h, you need Int32::Parse.

General advice for everybody who starts working in C++/CLI: try C# first. There is no need to make Windows Forms application in C++/CLI. C# is much better for this purpose. C++/CLI should be used for interoperability, accessing unmanaged resources and legacy C++ code.

05.12.2006 at 10:11AM PDT, ID: 16669325

Mahmoodaman:

I am trying this on a form with just a textbox (named textBox1) and a button. Here is the code of the button:

private: System::Void button1_Click(System::Object^ sender, System::EventArgs^ e) {
      int x;
      x = Int32::Parse(textBox1->text);

       }

This produces the following error:
error C2248: 'System::Windows::Forms::Control::text' : cannot access private member declared in class 'System::Windows::Forms::Control'

As for C#, is it of the same processing speed as C++? Actually, I have written a program in VB (where life is much easier!). But I am having a problem with its speed. I decided to convert it into C++ as it is the fastes programming language ,as far as I know.

So, how is the speed of C# copmared to C++?

Many Thanks

05.12.2006 at 10:16AM PDT, ID: 16669354

Mahmoodaman:

Sorry!
it is my mistake. I wrote "text", instead of "Text" here (it is the VB effect!)

Now how to deal with a float? and how is the speed of C#?

Sorry once again. . .

05.12.2006 at 10:41AM PDT, ID: 16669550

Rank: Wizard

AlexFM:

Use Convert.ToSingle Method (String) method. It parses string and converts it to float value.
Convert class contains set of function for parsing all basic types.

float f;

try
{
f = Convert::ToSingle(textBox1->Text);
}
catch (FormatException^ e)
{
// handle error
}
catch (OverflowException ^ e)
{
// handle error
}

05.12.2006 at 10:52AM PDT, ID: 16669643

Rank: Wizard

AlexFM:

About C++/CLI vs C#.
.NET contains number of languages: C#, VB .NET, C++/CLI etc. C# is better choice for programmer with C++ experience. VB is a good choice for VB6 programmer, though it looks like VB6, this means, not like "real" programming language. Microsoft encourages developers to work in C#, and gives better IDE support for this language. Some advanced language features of C# are not available in VB. C++/CLI has the same strength as C#, but it's syntax is more complicated and less readable. Create C# Windows Forms application and C++/CLI application, and you can see that C# looks much better.
All .NET languages are translated to the same intermediate langaage: MSIL. Different compilers (C#, BV, C++) convert source code to the same language. Performance of all .NET languages is absolutely the same.

So, why we need C++/CLI at all? It's strength is in interoperability. This language allows to call unmanaged code directly, which is impossible in C#. This allows to use legacy C++ code, access low-level API, write real time applications with hardware access, make time critical operations in unmanaged code. Here is the strength of C++/CLI. I beleive that we don't need C++/CLI unless we must do some unmanaged tasks.

05.13.2006 at 07:04AM PDT, ID: 16673841

Mahmoodaman:

Thank you for your reply AlexFM,

"Performance of all .NET languages is absolutely the same."

Does it mean that the running speed of a program built in C++ is the same as one built in VB?

Regards,

05.13.2006 at 07:12AM PDT, ID: 16673864

Rank: Wizard

AlexFM:

Yes. To be presize: performance of programs written in C++/CLI, VB .NET and C# is absolutely the same.
I am not talking about: unmanaged C++, VB6 - these are different languages.

Accepted Solution

05.13.2006 at 10:45AM PDT, ID: 16674566

Mahmoodaman:

I find this really strange! If I knew this, I would have gone for VB.NET inctead of C++!

I will look into this.

Thanks a lot AlexFM

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