declare/initialize int?

declare/initialize int?

• Maximasshel

  Jonathan,
  
  I got there just before your message - largely by trying anything I could think of!
  
  Thanks
  
  Geoff

  
  

• Kunle

  Jonathan,
  
  Many thanks for your suggestions - I will come back to them in a minute as although I have got that part of the code to work I am not sure why so will look carefully at your code  ...
  
  I am being held up at the moment as not sure how to write to a file. In C# I would use
  
  TextWriter tw = new StreamWriter("d:\\path\\file.txt");

  tw.WriteLine("fred");

  tw.Close;

  What is the C++ equivalent for Visual C++

  heers

  Geoff
  

  
  

• Newbe

  Geoff: it is probaly my fault but it is still not clear to me exactly what you are asking. I don't know if it is of any help but I would translate the above C# code as follows:
  
  // data members
  private:
     array<String^>^ myQuestion;
     array<String^>^ results;
     int qnumber;
  
  // constructor
  MyClass::MyClass()
  {
     myQuestion = gcnew array<String^>(2);
     myQuestion[0] = "question 1";
     myQuestion[1] = "question 2";
  
     results = gcnew array<String^>(myQuestion->Length);
     qnumber = 0;
  }
  
  // initialize label
  this->label->Text = myQuestion[qnumber];
  
  // record answer and update label
  results[qnumber] = trackBar->Value->ToString();
  ++qnumber;
  this->label->Text = myQuestion[qnumber];
  
  
  
  

• m.zirino

  Geoff: this looks like you have a value-type instead of a reference type: in this case you need to use '.' to access the members instead of '->'
  
  

• Colin F

  Jonathan,
  
  I'm going round in circles with this one! When I look at the Events properties for the Track Bar I see that the name to the right of the Scroll behaviour property is trackBar1_Scroll so if I just wish to print out this value, forgetting putting it into an array for the moment, what would I use
  
  Is there an equivalent to the C# MessageBox.Show Or how do I print to the Console
  
  Cheers
  
  Geoff
  
  
  
  
  
  

• alkaline

  Jonathan,
  
  Thanks for the TextWriter code. I must be nearly there but getting a couple of error messages.
  
  line 155   error C2227 left of '->ToString' must point to class/struct/union/generic type
  line 181   error C2228 left of '.Close' must have class/struct/union
  
  I have following for initialization which I think is OK.
  
  

  private: static array<String^>^ LHSquestions = gcnew array<String^> {"question 1", "question 2"};

  private: static array<String^>^ RHSquestions = gcnew array<String^> {"question 1", "question 2"};

  private: static int qnumber = 0;

  private: static array<String^>^ results = gcnew array<String^> [LHSquestions->Length];
  
  
  
  and for the first error message
  
  this->results[qnumber] = trackBar1->Value->ToString(); // line 155
  
  
  
  and for the second error message
  
  TextWriter^ outfile = gcnew StreamWriter("h:\\a-temp1\\data.txt");

  for (int i=0; i < LHSquestions->Length; i++) {

   outfile->WriteLine(results);

  }

  outfile.Close();  // line 188
  
  
  If this not clear I can post the whole code!
  
  Cheers
  
  Geoff

  
  

• JedG

  Jonathan,
  
  having gone back a step and just used Console::WriteLine("fred"); to ceck the correct way to print out anything (!) I am now getting an error from earlier in the code.
  
  I have
  
  

  private: static array<String^>^ LHSquestions = gcnew array<String^> {"question 1", "question 2"};

  private: static array<String^>^ RHSquestions = gcnew array<String^> {"question 1", "question 2"};

  private: static int qnumber = 0;

  private: static array<String^>^ results = gcnew array<String^> [LHSquestions->Length];
  
  and the last line is intended to create the results array with the same number of elements as in LHSquestions - this seems to be wrong. Am I able to do this
  
  Cheers
  
  Geoff

  
  

• khandar

  Jonathan,
  
  re my message with the 2 errors - have found the cause of the 2nd one - I had outfile.Close() instead of outfile->Close()
  
  also found error in the other code but still get 2 similar error messages
  
  results[qnumber] = trackBar1_Scroll->Value->ToString();
  
  (I had trackBar1 not trackBar1_Scroll)
  
  error messages re above
  
  error C2227: left of '->Value' must point to class/struct/union/generic type
  error C2227: left of '->ToString' must point to class/struct/union/generic type
  
  thought
  
  Cheers
  
  Geoff
  
  
  

• Drickus

  Jonathan,
  
  I may be asking the wrong question!
  
  In my app I am aiming to put the trackbar position value into an array each time the user clicks on  button to move to the next question where he/she will be asked to position the trackbar again as a response to the question.
  
  In Visual C# I have
  
  private string[] myQuestion;
  private string[] results;
  private int qnumber = 0;
  
  myQuestion = new string[]{"question 1","question 2"};
  results = new string[myQuestion.Length];
  
  Then I position the first question
  
  this.label.Text = myQuestion[qnumber];
  
  When the button is clicked the trackbar value is put into the results array, qnumber is increased by 1 and a new question is display.
  
  results[qnumber] = trackBar.Value.ToString();
  ++qnumber;
  this.label.Text = myQuestion[qnumber];
  
  after the last question all the members of the results array are written to a file.
  
  Is this any clearer !
  
  Cheers
  
  Geoff
  
  
  
  

• MikeFesta

  Hi Geoff: I'm not sure I 100% understand your question.
  
  In C++ (and C) there is no built-in way in the language to get the size of an array; you either need to use the size that the array was declared with or use one of the many language "tricks" that will give you the size of an array.
  
  Given an array declaration like:
  
  const int SIZE = 10;
  
  int myArray[SIZE];
  
  I would iterate through the elements of the array using one of the following snippets:
  
  for (int k = 0; k < SIZE; ++k)
  {
     myArray[k] = ...
  }
  
  for (int k = 0; k < sizeof(myArray)/sizeof(myArray[0]); ++k)
  {
     myArray[k] = ...
  }
  
  #include <stdlib.h>
  
  for (int k = 0; k < _countof(array); ++k)
  {
     myArray[k] = ...
  }
  
  _countof is a macro that gives you the number of elements in an array. It is defined in stdlib.h
  
  
  
  

• Dennis G.

  Yes: you are able to do this but the last line should be:
  
  private: static array<String^>^ results = gcnew array<String^> (LHSquestions->Length);
  
  
  
  

• Fraser Putnam

  When it comes to writing managed code with C++ the code is remarkably similar to the equivalent C# code. One of the biggest differences is that C++ keeps the syntactic difference in referring to an object on the stack and an onject on the heap.
  
  So the code above would be translated to:
  
  TextWriter^ tw = gcnew StreamWriter("D:\\path\\file.txt");
  
  tw->Write("barney");
  tw->Close();
  
  As you can see the code is remarkably similar: the major difference is the use of ^ and -> and these are used because the StreamWriter object is created on the GC heap (via gcnew).
  
  
• declare/initialize int?