Need Help

I don't know why you still keep refusing to depict in pseudo code what you program is supposed to do... :rolleyes:

However, here is what it does so far:

Code:

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- calculate sin(PI/2) and store it in y
- calculate the sinus of an uninitialized angle variable and
  store it in sin_of_angle (which now contains an arbitrary
  random value)
- draw a T-shaped coordinate cross
- if Sin was chosen:
  - count i up from 0 to count (another uninitialized variable)
- do nothing else with i (it is completely useless, as is the loop)

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I don't know if that's what you intended, but I don't think so, as it is still very far from anything that would draw a graph. The various values are completely unreleated here. What's the role of i, and what is count? What's the point in using a variable who's value has never been set to anything meaningful for calculating another value?

Code:

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double PI = 3.1415926535;
 int count;
    int i;
    double angle;
double x, y;
    x = pi / 2;
    y = sin(x);
//angle = ??? it's not initialized!
      double sin_of_angle = sin(angle);
    pDC->MoveTo(60, 150);
 pDC->LineTo(60, 300);
 pDC->LineTo(575, 300);
 pDC->MoveTo(60, 300);
 pDC->LineTo(60, 450);
 
//who is m_Chart ??? 
 switch (m_Chart) {
   
 case Sin:
//who is count. count = ??? it's not initialized
//what do you do with this for??? nothing i see.
          for(i = 0; i < count; i++);

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are you aware of what you are supposed to do? i think not!
why do you keep ignoring gstercken advices?
do you know how to write pseudocode? if yes, then do it.

please clarify all these things to yourself and to us and then you might get useful help.

okay here is what it's supposed to do. I've not written psuedocode before.

-Draw a graph
-enter number to calculate
- if either the sin or cos button is pressed
-calculate the value entered and draw lines based on the number entered.

OK, now let's have a look at what you specified. First of all, you state that you start by drawing a graph, but I assume that you just mean drawing the coordinate system (as for drawing the graph, you need the number entered in the second step).
Step two, "enter a number to calculate" is already done by the DDX mechanism, I think it is safe to assume that you already have the number (more specifically, the number of samples to be used to draw your graph, that's important) in m_iSamples.
Step three describes the reaction to clicking one of the buttons. You didn't post the code, but I assume that the handlers for the two buttons just set the value of m_Chart to Sin or Cos, respectively, and invalidate the view to have it redrawn, so we can fully concentrate on step 4, the part actually missing from your implementation so far: "calculate the value entered and draw lines based on the number entered". Now that's a little vague, and you should probably break it down further.
You are actually describing two large, distinct steps here:

1. calculate the value entered
2. draw lines based on the number entered

As to 1.: The value entered is already in m_iSamples, so it doesn't need to be calculated. What do you need to calculate instead, and how does this depend on the number entered?
As to 2.: This step is described very vaguely, so you should try to further break it down into several steps. What lines do you want to draw, and how do they depend on the number entered? Where are the sin and cos in this description, and where is the loop?

I'll break it down even further once I get home to exactly what I am trying to accomplish. Oh yea I'll post the code for m_Chart and more importantly what it is.

Okay I'll break it down further.

-use the MFC app wizard
-add variables and message handlers
-user enters number of samples to draw example 8
-user presses the sine button
-use 8 lines to draw the sine curve.
-graph the sine and/or cosine function
-x axis will start at 0 and end at 2 p radian measures
-y axis will run from 1 to -1
- define p as double 3.1415926535
- scale the x,y values to match the display
- use m_chart to determine which button was selected
this is what I have to create the m_chart variable
class CProject5View : public CFormView
{
protected: // create from serialization only
CProject5View();
DECLARE_DYNCREATE(CProject5View)
enum {Sin, Cos} m_Chart;

Well, let's see how to go about this...

Now, what you listed so far is not a further breakdown of the "draw lines" step, but rather a collection of various items. Note that pseudocode should describe what the program (or rather a part of it) is supposed to do, not what you should do. The following items, however, describe what you have to do, making it sound much like a homework assignment... ;):

-use the MFC app wizard
-add variables and message handlers

The next two items, OTOH, describe a possible scenario of what the user of your program might do, not what the program does:

-user enters number of samples to draw example 8
-user presses the sine button

The following items, in turn, don't describe what happens, but are rather constraints to be applied. They have nothing to do with pseudocode, but are important nonetheless:

-x axis will start at 0 and end at 2 p radian measures
-y axis will run from 1 to -1
- define p as double 3.1415926535

Finally, these items are actually part of the process of drawing the graph:

- scale the x,y values to match the display
- use m_chart to determine which button was selected
- graph the sine and/or cosine function
- use 8 lines to draw the sine curve.

The first is very important and was missing from your description so far. It brings us to the fact that you are actually dealing with two coordinate spaces here:

1. The logical coordinates, which range from 0 to 2*PI (x) and -1 to 1 (y) as described above, with the origin at (0,0)
2. The screen or window coordinates used for drawing, which are pixels in your case. Note that the way you draw the axes imply that screen coordinates range from 60 through 575 for x and from 150 to 450 for y, the origin being at (60,300).

It should be obvious that you need the screen coordinate limits for drawing the axes and for plotting the graph, so you should better define them as constants (we could use 'S' to denote them as being Screen coordinates):

Sx0 = 60 (x origin)
SxExt = 515 (extent of the x axis)
Sy0 = 300 (y origin)
SyExt = 150 (extent of the y axis)

From these, we can derive additional useful constants to be used in drawing:

SxMin = Sx0 (minimal x screen value)
SxMax = Sx0 + SxExt (maximal x screen value)
SyMin = Sy0 + SyExt (minimal y screen value)
SyMax = Sy0 - SyExt (maximal y screen value)

Note how the '+' and '-' signs are used to calculate SyMin and SyMax, this is because the y axis in screen coordinates extends downward (as often in computer graphics). Now casting that into C++ code is pretty straightforward. As you started using the 'i' prefix for integer variables, we will continue doing so:

Code:

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const int iSx0  = 60;  // x origin
const int iSxExt = 515; // y origin
const int iSy0  = 300; // extent of the x axis
const int iSyExt = 150; // extent of the y axis

const int iSxMin = iSx0;          // minimal x screen value
const int iSxMax = iSx0 + iSxExt; // maximal x screen value       
const int iSyMin = iSy0 + iSyExt; // minimal y screen value
const int iSyMax = iSy0 - iSyExt; // maximal y screen value

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Using those constants, you can now rewrite the code for drawing the axes like this:

Code:

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// Draw X axis:
pDC->MoveTo(iSx0,  iSy0);
pDC->LineTo(iSxMax, iSy0);

// Draw Y axis:
pDC->MoveTo(iSx0, iSyMax);
pDC->LineTo(iSx0, iSyMin);

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Note how this makes much clearer what your MoveTo / LineTo calls actually do. Also, if you want to change the position or size of the screen coordinate space later, you just need to modify the base constants. You could even make them variables in the future, and automatically scale the coordinate space depending on the current windwow size if you like.

Next, you need to plot the graph. Think a moment about what 'plotting a graph' actually means: Taking a series of x values, calculating the corresponding y value for every x value, and drawing a line to the point given by (x, y). Now, how do you get a 'series of x values'? Probably by using a loop which starts at some x value and increments that by some step value until the maximal x value is reached. Now, in your case, you have three concurring parameters which could possibly define the range of x values: The logical coordinate space (0 through 2*pi), the screen coordinate space (iSxMin through iSxMax) or the sample count (0 through 8, note that you need 9 samples to draw 8 lines). Each of the three could be used as the loop counter, giving you the following three options to build the loop:

1. Your loop counter is a real number starting at 0 and ending a 2*PI. The increment to be used in each iteration is 2*PI divided by the number of samples. In each iteration, calculate the sin (or cos) from the x value, transform logical x and y values to screen coordinates, and draw the line.
2. Your loop counter is an integer variable representing the screen x coordinate, starting at iSxMin and ending at iSxMax. The increment to be used is iSxExt divided by the number of samples. In each iteration, calculate the logical x value from the screen x value. Calculate the logical y value as sin(x) or cos(x), transform it to screen coordinates, and draw the line.
3. Your loop counter is the sample index, starting at 0 and ending at m_iSamples. For each sample, you calculate the logical x value for that sample, and the corresponding y value using sin() or cos(). Then you transform them to screen coordinates and draw the line.

Now which option you choose is up to you, however, due to possible double / integer conversion effects, I would suggest you use option C (without elaborating further on that here).

Now, having paved the way so far I would like to leave that task to you: Write the loop as pinpointed in option C. Use the constants defined above to convert between sample index, logical coordinates and screen coordinates. If you have questions, ask.

wow, what an explanation !!!
i wish someone would have thought me like this when i first started doing stuff in C++ :D :)

It's not a homework assignment I have this book and it's one of the excercise problems. I wanted to try and do.Yea thanks for the explanation hopefully I can get this it's rather frustrating. I will ask you have been most hopefull.

Quote:

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Originally posted by JerryShane
Yea thanks for the explanation hopefully I can get this it's rather frustrating.

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Well, it shouldn't be frustrating. It's a classical programming task which is fairly straightforward to implement - the important thing is to analyze the problem correctly, that is, to get a clear and detailed idea of what should happen, and then come up with a likewise detailed solution of how it should happen. I hope the above helps you to get the point.

Yes it does thsnks for your help I'll be in touch if I have any more questions. You're right it shouldn't be frustrating.