Math Operation in Windows Form Application

Question

I am trying to use a function in windows form application that convert a given point to another coordinate system. However, I encountered a strange problem. The input are correct but output is always 0. First, I thought it caused because of the local variables and then instead of variables I used only integers but it did not solve. I have no idea about it. Here the code and output basically:

string[] newPoint1 = convertPoints(X1, Y1);

string[] convertPoints(int oldX, int oldY)
        {
            //int newX = ((oldX - oldLeft) / (oldRight - oldLeft)) * (newRight - newLeft);
            MessageBox.Show(oldX.ToString());   // output is 296 
            int newX = (oldX / 500) * 4096;   // ?????????????????????  (296/500) * 4096  = 0 ?????????????
            MessageBox.Show(newX.ToString()); // here output is 0
            int newY = newTop + ((oldY - oldTop) / (oldBottom - oldTop)) * (newBottom - newTop);
            
            //MessageBox.Show(newY.ToString());
            string[] newPoints = {newX.ToString(), newY.ToString()};
            //MessageBox.Show(newPoints[0], newPoints[1]);
            return newPoints;
        }

score 1 · Accepted Answer · answered Dec 22 '21 at 14:08

This is working as it should. Because oldX is an Integer, when you divide it, it rounds (drops anything after the decimal). I would convert it to float and back into an integer, like so

int newX  = (int)(((float)oldX / 500) * 4096);

This will preserve the whole number until you're done at the end. You'll also need to do the same for the Y values

Daniel Kelsch · Answer 2 · 2021-12-22T14:12:51.387

You are getting 0 because oldX/500 is a fraction usually and since you are using the int datatypes there can only be whole numbers. What I would recommend doing is changing the data type then rounding yourself.

  //Old code
  int newX = (1 / 500);
  Console.WriteLine(newX);
  // writes 0 to console


  //New code
  double newXD = (1 / 500.0) * 4096;
  Console.WriteLine(newXD);
  //Writes 8.192

The 1 and the 500 are considered ints try

Console.WriteLine(1/500);

It writes 0 to the console.

Console.WriteLine(1/500.0);
Console.WriteLine((float)1/500);
Console.WriteLine((double)1/500);

All these write 8.192 to the console.

Then after you have the double or other more accurate data type consider rounding if you really want an int.

score 0 · Answer 3 · answered Dec 22 '21 at 14:08

0

An integer division cuts off the decimal places. So in your case, 296/500 you would expect 0.592. As integer has no decimal places, it cuts off them off resulting in 0.

Change the oldX to double and divide by 500.0

answered Dec 22 '21 at 14:08

Marcii

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Math Operation in Windows Form Application

3 Answers3