Sierpinski Triangles. Have a few questions.

[xdrazkalnytex]

So I was working on this program call Sierpinski Triangles. The program is working but doesn't seems to be right.
When I run the program "java Sierpinski Triangles 4" I got one big triangle as the output. Am I doing something wrong here?

// SierpinskiTriangles.java

public class SierpinskiTriangles
{
    // Recursively draws Sierpinski triangles. The argument n specifies the 
    // recursion depth. The rest of the arguments are the (x, y) coordinates 
    // of the vertices of an equilateral triangle; a being the bottom left vertex, 
    // b the bottom right vertex, and c the top vertex.
    private static void draw(int n, double ax, double ay, double bx, double by, 
                             double cx, double cy)
    {
        // TBD
      double x = 0.0;
      double y = 0.0;
      
      double[] xs = {ax , bx , cx};
      double[] ys = {ay , by , cy};
      
      for(int i =0; i < n; i++);
      {
        int k = StdRandom.uniform(1);
        if(n ==0)
        {
          double x1 = (xs[k] * x) + (xs[k] * y) + (xs[k]);
          double y1 = (ys[k] * x) + (ys[k] * y) + (ys[k]);                    
        }
      }
      StdDraw.polygon(xs,ys);
    }

    // Entry point.
    public static void main(String[] args)
    {
        int n = Integer.parseInt(args[0]); // Recursion depth.
        StdDraw.setXscale(0.0, 1.0);
        StdDraw.setYscale(0.0, 1.0);
        StdDraw.show(0);
        draw(n, 0.0, 0.0, 1.0, 0.0, 0.5, 0.866);
        StdDraw.show(0);
    }
}

[Fubarable]

So I was working on this program call Sierpinski Triangles. The program is working but doesn't seems to be right.
When I run the program "java Sierpinski Triangles 4" I got one big triangle as the output. Am I doing something wrong here?

// SierpinskiTriangles.java

public class SierpinskiTriangles
{
    // ****Recursively****  draws Sierpinski triangles. The argument n specifies the 
    // recursion depth. The rest of the arguments are the (x, y) coordinates 
    // of the vertices of an equilateral triangle; a being the bottom left vertex, 
    // b the bottom right vertex, and c the top vertex.
    private static void draw(int n, double ax, double ay, double bx, double by, 
                             double cx, double cy)
    {
        // TBD
      double x = 0.0;
      double y = 0.0;
      
      double[] xs = {ax , bx , cx};
      double[] ys = {ay , by , cy};
      
      for(int i =0; i < n; i++);
      {
        int k = StdRandom.uniform(1);
        if(n ==0)
        {
          double x1 = (xs[k] * x) + (xs[k] * y) + (xs[k]);
          double y1 = (ys[k] * x) + (ys[k] * y) + (ys[k]);                    
        }
      }
      StdDraw.polygon(xs,ys);
    }

    // Entry point.
    public static void main(String[] args)
    {
        int n = Integer.parseInt(args[0]); // Recursion depth.
        StdDraw.setXscale(0.0, 1.0);
        StdDraw.setYscale(0.0, 1.0);
        StdDraw.show(0);
        draw(n, 0.0, 0.0, 1.0, 0.0, 0.5, 0.866);
        StdDraw.show(0);
    }
}

Note the word highlighted by the **** **** -- your comments state that this is supposed to be an example of recursion. So where is your recursion?

[sunde887]

First, I don't see any recursive calls. Also, in the loop in draw you create local variables in the loops body and never use them.

[xdrazkalnytex]

So does that mean I dont need a loop?
I didn't know there was a recursive, when I first got the file for this program I just fill out the body.
Also, recursive means the triangles supposed to draw 3 more triangles inside of the large one right?
Can someone help me with the recursive calls since I have no idea how to get started.
Thanks!

[sunde887]

Using recursion is a general practice, which is common in mathematics, as well as computer science. Recursion is the process of defining a base case and giving a rule which uses previous terms. As a concrete example, here is a recursive definition of n! (n factorial)

public int factorial(int n){
  if(n == 0){
    return 1;
  }
  return n * factorial(n - 1);
}

With each iteration you perform a smaller sub task. Generally, loops aren't used in recursion. Perhaps for the recursive definition of Sierpinski, you may stop when n reaches a certain depth, and each depth will call on itself to draw three sub Sierpinski triangles inside of the initial one.

[xdrazkalnytex]

how would I start my recursive for this program?
the public int......can't be place at the beginning of the program.