How do I call something in to a for loop?

[slenish]

Hi im new to C++ and im trying to call a function in to a for loop.

[B]void DrawLine[/B](int x1, int y1, int x2, int y2, unsigned int color)
{

int dx, dy;                         // dy / dx is the slope
    int x, y;                           // loop and point variables

    // calculate changes in y and x between the points
    dy = y2 - y1;
    dx = x2 - x1;

    if (Abs(dy) > Abs(dx)) {
        // since there is a greater change in y than x we must
        // loop in y, calculate x and draw
        for (y=y1; y != y2; y += Sign(dy)) {
            x = x1 + (y - y1) * dx / dy;
            PGraphics->AddPoint(x, y, color);
        }
    }
    else {
        // since there is a greater (or equal) change in x than y we must
        // loop in x, calculate y and draw
        for (x=x1; x != x2; x += Sign(dx)) {
            y = y1 + (x - x1) * dy / dx;
            PGraphics->AddPoint(x, y, color);
        }
    }

    // draw the last pixel
    PGraphics->AddPoint(x2, y2, color);

    // draw the points
    PGraphics->Draw();
}


void DrawStuff() {
    COLORREF green = RGB(0, 255, 0);     // green color to draw with
    COLORREF purple = RGB(255, 0, 255);  // purple color to draw with

    char str[32];                       // string to store user input
    int h, k;                           // parabola vertex
    double a;                           // parabola constant - might be a decimal
    int x, y;                           // loop and point variables
    int xPrev, yPrev;                   // previous point for drawng line segments
    int ymin, ymax;                     // limits for y loop
    RECT rect;                          // rectangle for the output window

    // get the user input from the edit boxes and 
    // convert string input to integer
    GetDlgItemText(HDialog, IDC_EDIT_VERTEXX, str, 32);
    h = atoi(str);
    GetDlgItemText(HDialog, IDC_EDIT_VERTEXY, str, 32);
    k = atoi(str);
    GetDlgItemText(HDialog, IDC_EDIT_CONSTA, str, 32);
    a = atof(str);                              // use atof to allow user to enter a decimal

    // get the rect for this window
    GetClientRect(HOutput, &rect);

    // use the rectangle info to set up y loop limits
    ymin = -(rect.bottom - rect.top) / 2;
    ymax =  (rect.bottom - rect.top) / 2;

    // clear the scene and add an axis
    PGraphics->ClearScene(RGB(0, 0, 0));
    PGraphics->AddAxis(RGB(150, 150, 150), 10);

    yPrev = ymin;
    xPrev = (int)( a * (yPrev-k) * (yPrev-k) ) + h;

    // loop in y, calculate x and draw
   [B] for (y = ymin; y <= ymax; y++) {
        x = (int)( a * (y-k) * (y-k) ) + h;
        PGraphics->AddPoint(x, y, green); [/B]
    }

    // draw the points
    PGraphics->Draw();
}

What im trying to do is take the DrawLine function (that I put in bold) and have it referenced right before the for loop in the DrawStuff (that i put in bold) This way the DrawStuff will know to use DrawLine to draw more points in a line.

Thanks in advance!

[weaknessforcats]

The only wat that DrawStuff can know to use DrawLine is for you to a) call Drawline inside DrawStuff or b) have a function pointer argument in DrawStuff that contains the adress of the correct DrawLine function.

void DrawStuff()
{
     DrawLine(etc...);
     for (etc...
     {
         ///or  DrawLine(etc...);
     }
}

[whodgson]

Do you mean to spell ymin like ymi.n

[slenish]

Hi weaknessforcats ,
Appreciate you helping me out with this I was wondering if you could give me a little more detail if your example or possibly give me a couple websites with some examples I could look at.

Thanks for the help!


Whodgson,
its supposed to be ymin. :) It refers to the min value of y

[weaknessforcats]

Hi weaknessforcats ,
Appreciate you helping me out with this I was wondering if you could give me a little more detail if your example or possibly give me a couple websites with some examples I could look at.

It may be you are no clear on how a function call works.

Your program excutes statements in sequence. A B C D. If you have steps that are used in several places, you code A XXX B XXX C XXX D XXX. Those XXX instrcutions are repeated as many times a needed.

A function call is a way of coding XXX only once. These instructions are put together using a name an argument list and a pair of braces:

void MyFunction()
{
      XXX

}

The code now looks like:

A MyFunction() B MyFunction() C MyFunction() D MyFunction().

The last thing is when you use a variable as an argument to a function, the compiler makes a copy of it. The copy is the argument variable of the function being called. This is done to protect the original variable.

You can find all sorts of information about this from just about any book on C.