Thread: Grid problem

Show us an attempt and we will help you. I am presuming that your program will be console based since you want to display one of three symbols at each point. On that basis, I will give you a hint: Think about your the console 'grid' as your coordinate system. You can test where a point is in/near the circle using Pythagoras' theorem.

edit: By the way, this recent thread might prove to be helpful: drawing a circle in C

Start with what you know you'll need - he grid (aka 2D array[][]). Your data type will be type char, and what angle are you drawing this wheel/tire from - side, top, or what? I would choose side, but whatever your prof wants.

++ looks like tread, and $$$ looks like where the tread meets the sidewall. Maybe use * for the sidewall itself. I'm just throwing out ideas here.

As for the wheel itself, you'll put every char onto the grid, based on it's distance from the center. That's where the Pythagorean theorem comes in.

Say I want to know what char goes at row3, column (col) 1, and the center is at 10, 10. So I work out my equation to find that distance from that square to the center:

distance² (hypotenuse) = height² + base², so

d² = (10-3)² + (10-1)² (Note: always a positive number for height and base)
d² = 49 + 81
Distance = 11.4 and round it down to 11, since char's can't be less than whole integers

So if I want the center to the end of the start of the sidewall to be 12, then it gets the char for the inside portion of the wheel or tire, not the char for the sidewall.l

I didn't mention the absolute value part of the math for it:

Where "base" is the int length of the base of the triangle, "height" is the height, and i is just a temporary long int. "hyp" is the hypotenuse.

Cx = x value of the center point of the wheel (horizontal position on screen)
Cy = y value of the center point of the wheel (vertical position on the screen)


Without the " * 2.7", my tires look more like eggs The right number here, depends on what font size
you use, in your console window.

Code:

      base =abs(c - Cx);
      height = abs(r - Cy) * 2.7; //2.7 was the best for my screen
      i = (base*base) + (height*height);
      hyp = sqrt(i);
      if(hyp < 0) putchar('8');
      if(hyp > Tread || hyp <= Inside) w[r][c]=' ';
      else if(hyp <= Tread && hyp > Scruff) w[r][c]='$';
      else if(hyp <= Scruff && hyp > Sidewall) w[r][c]='+';
      else if(hyp <= Sidewall && hyp > Inside) w[r][c]='*';

Tread is a define for the most outward portion of the tire, then Scruff, then Sidewall, and finally Inside.

You have to include <math.h> for abs() and sqrt().

You have include an 'x = 0;' statement in your for loops for some reason. Given where it is, this is unnecessary - it does nothing.

Anyway, don't let that put you off, you are definitely making progress but you should do something like this for your if statements:

Code:

c_squared = pow(x - 24, 2) + pow( y - 24, 2);

if( c_squared > r1*r1 )
{
    /* Draw some stuff here */
}

By the way, have you considered what will happen if the values of r1 and r2 are greater than 50?

Edit: General equation for a circle in Cartesian coordinates is:

r^2 = (x - x0)^2 + (y - y0)^2

Where x0 and y0 are the coordinates of the centre.

Further Edit: If you want your wheel to appear central in your grid it might be worth making your grid an odd size. E.g. Instead of doing a 50 by 50 grid, do a 51 by 51 or 49 by 49 grid, because that way the centre point will appear 'even'. If you don't know what I mean, you will when you start drawing stuff.

The grid is just:

Code:

Your #includes up here: stdio.h and math.h

#defines down here: I used Cx (x value of the center point), and 
Cy (vertical value of the center point. 

Several others for Tread, Sidewall, Inside, etc., parts of the tire. 
And ROWS and COLS for the array itself. 

I moved the center of the tire from 10,10 to 12, 30 so it
could be better centered, and let me draw a bigger tire.

I used long int's for i, c, base, height, hyp.


char w[ROWS][COLS];  //declare the w(heel) array

for(r=0; r < ROWS;r++)  {
  for(c=0; c<COLS; c++)  {
      //arithmetic in here
      if(hyp > Tread) w[r][c] = ' ';  //a blank space for outside the tire
      else if(hyp <= Tread and > Sidewall) w[r][c]='$';
      else if(hyp .... etc. like that. Step down through every part of the tire.

   }
  printf("\n");
}

All calculations are done, now draw it.
for(r=0; r< ROWS;r++)
  for(c=0; c<COLS;c++) 
    printf("%c", w[r][c]);

That's really all there is to it. Hard part is getting the math to work out, since the fonts are usually NOT square. (as noted in the previous post).

No distance to the center equations? I don't get that. IMO, you *have* to have a distance equation from the center of the wheel, to the square on the grid.

How could that program ask you for a filename?

Let's see what it draws. That's not what you want, imo.

I think what they were going for was something like this: The "font factor" needs to be bumped up a bit, since it's still a bit egg-shaped, but it's easily fixed.