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Hi, I am new to CLI-Windows Forms programming and I need to perform this simple task:
1) Allow the user to enter a value in a Text Box (textBox1)
2) Assign such value to a variable of type double (variable1)
[I am having difficulties casting the string to double]
3) Perform computations on that variable
[I should be able to do this once it's a double]
4) Display the resulting value in another Text Box (textBox2)
Can someone be so kind to help me with the correct syntax I should use for each step?
Many thanks.
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Thanks for the advice, it works. But I obviously get a crash when I leave the text box empty or I enter a non numerical value.
Here is the code I use to assign the value entered in the text box (as string) to a type double variable:
//
variable1 = double::Parse(textBox1->Text);
//
How can I solve this? Thanks!
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J_E_D_I wrote: But I obviously get a crash when I leave the text box empty or I enter a non numerical value.
Use TryParse().
Mark
Mark Salsbery
Microsoft MVP - Visual C++
![Java | [Coffee]](https://codeproject.freetls.fastly.net/script/Forums/Images/coffee.gif)
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I have tried:
//
double number;
variable1 = double::TryParse(textBox1->Text, number);
//
With the code above it's better and the program does not crash anymore.
However the problem is not completely solved because when I leave the text box empty or enter a character different from a number, the result of variable1 is zero, which causes an error in the calculation that follows.
How can I show an "Error" message when this has happened?
Alternatively, is there any way that I could make the textBox accept only numerical values and display an error in the other cases?
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TryParse returns a bool.
double variable1;
if (double::TryParse(textBox1->Text, variable1))
{
}
else
{
}
Did your Visual Studio not come with MSDN library? 
Mark
Mark Salsbery
Microsoft MVP - Visual C++
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This is a fantastic answer! Thank you so much, it solved the problem.
Mark Salsbery wrote: Did your Visual Studio not come with MSDN library?
Probably you guys super expert programmers manage to find what you are looking for in MSDN. I program in my spare time just for fun and I do not find them helpful AT ALL!!  They seriously lack of simple examples for beginners like me and they take too much for granted. Regarding TryParse there was no specific example for c++.
Cheers!
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J_E_D_I wrote: there was no specific example for c++
Hint: Use the C# examples. For most examples of using .NET framework classes, the only
difference will be
'->' in c++ instead of '.' in c#
gcnew in c++ instead of new in c#.
Cheers! ![Beer | [beer]](https://codeproject.freetls.fastly.net/script/Forums/Images/beer.gif)
Mark
Mark Salsbery
Microsoft MVP - Visual C++
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J_E_D_I wrote: Hi, I am new to CLI-Windows Forms programming and I need to perform this simple task:
See if this helps[^]
led mike
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Awesome!
Mark Salsbery
Microsoft MVP - Visual C++
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Mark Salsbery wrote: Awesome!
Nah, that was mildly amusing. This is awesome.[^]
led mike
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Indeed! 
Mark Salsbery
Microsoft MVP - Visual C++
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Hi,
I am new to Visual C++/.Net, I have a simple question. I have a DateTimePicker object which I need to display future date in days (i.e. if you pick 11/21/2009, I will display 365 days).
I have managed to compute my 365 days and converted it to a char * but I am not able to assign the char* to the label Text i.e. Sysytem::String ^
Can anyone help me? Thanks in advance
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If you have a number, just call ToString() to get a System::String^
Christian Graus
Driven to the arms of OSX by Vista.
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niiAmoo wrote: I have managed to compute my 365 days and converted it to a char *
Why are you using char * in C++/CLI?
Mark Salsbery
Microsoft MVP - Visual C++
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Sorry, That was what I was used to  . I tried this code and it worked
TimeSpan expirationDay = expirationDateTimePicker->Value.Date - expirationDateTimePicker->Value.Now.Date;
expiration->Text = expirationDay.Days.ToString();
Thanks for your help
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Mark Salsbery wrote: Why are you using char * in C++/CLI?
nostalgia 
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because he is a real programmer that doesnt like to be "managed" 
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the ascii code of char '1' and int (1) has 48 numbers defrence
it means if you wanna change the char '1' to int 1 you should minus 48 from the ascii code !
it really works, i`ve test it
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Hi all.
Need some help please.
Does someone know how to display windows explorer window with specified path? Managed and unmanged variants is ok.
Thanks.
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Process.Start or ShellExecute with the path, should do it.
Christian Graus
Driven to the arms of OSX by Vista.
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Thanks very much. ShellExecute is ok.
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Hi there,
I am having some problems to create a dll file to use in my java application. Let me try to explain the scenario:
1.- Java GUI which uses JNI to call native C functions.
2.- This C functions uses C++ classes inside.
And at this moment i don't have the faintest idea of how to build a correct idea, so i would appreciate any help.
Thanks in advance,
Hector.
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i have solved the problem: these are the steps i have followed
1.- Create a java class with native methods. Create code to load the dll library.
Example:
import java.io.File;
/**
* @author hectorhg
*
*/
public class CLangWrapper {
/**
* Path of the .dll file
*/
public static final String dllName = "C:\\clangwrapper.dll";
// Code to Load the dll
static{
try{
File l_file = new File(".");
System.load(dllName);
}
catch (UnsatisfiedLinkError e) {
e.printStackTrace();
}
catch (Exception ex){
ex.printStackTrace();
}
}
/*********************************************
* N A T I V E M E T H O D S *
*********************************************/
/**
* Starts wrapper
* @return
*/
public static native int wrapperStart();
}
2.- javac myclass.java
3.- javah -jni package.myclass # in the ../ directory of package.
4.- A .h file is generated. implement it in a .c file.
5.- I have used vs2008, to create a dll project. In this project i included those files (don't forget about jni.h and jni_md.h) and my .cpp files.
6.- in the .c file implementing the native methods.
struct CPLUPLUSCLASS cppClass; // Global variable
#if defined(__GNUC__) && defined(_WIN32)
extern "C" JNIEXPORT jint JNICALL Java_sidsaTvAppControl_CLangWrapper_wrapperStart
(JNIEnv *, jobject){
#else
JNIEXPORT jint JNICALL Java_sidsaTvAppControl_CLangWrapper_wrapperStart
(JNIEnv *, jobject){
#endif
jint l_retVal = 0;
l_retVal = cppClass.myFunc();
return l_retVal;
}
7.- Note that the file that implements the .h file generated by jni must be included in the dll.
8.- compile and place the .dll into the rigth directory according to your java class implementation.
9.- run your java application.
10.- Check everything is working and smile 
I hope that this can help someone 
Regards,
Hector.
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Hi,
I am working on a C++/CLI project using winforms. I need to consume a 3rd party native C++ dll.
Can any one send me some sample code to do the same.
Thanks,
Pratap
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