Help with a Project for school.

I am not looking for a total answer for the problem. I have written some code and it is not working like it should. The basic problem is to make a simple pinball program. The outside limits are at x=30 to x=70 and y=10 to y=110. There is a function that has been provided for us, but i am not adding it to the code here just to simplify it. So, the ball starts on the line of y=10 and either bounces to the left or right and is supposed to reverse direction as soon as it hits the other walls. As soon as the ball hits y=10 then it stops.

hold on;

%This is the staring points x(1)=50; y(1)=10; %Direction in which the ball will move %right 1 %left -1 dx=1; dy=1; x_dir=[-1 1]; y_dir=[-1 1]; xdir=x_dir(randi([1,2],1)); ydir=y_dir(randi([1,2],1));

%while y(j)>=10 means game over, the other if statements are meant to bounce the ball off of that line.

j=1; while y(j)>=10; x(j+1)=x(j)+dx*xdir; y(j+1)=y(j)+dy*ydir; if x(j+1)<=70; xdir=-1; ydir=y_dir(randi([1,2],1)); end if x(j+1)>=30; xdir=1; ydir=y_dir(randi([1,2],1)); end if y(j+1)>=110; xdir=x_dir(randi([1,2],1)); ydir=-1; end

    plot(x,y,'bo');
    j=j+1;
end
hold off

I think my problem is at line 34. Which is: y(j+1)=y(j)+dy*ydir;

This line is saying the the y line can be either a negative direction or positive direction, but when the program starts it should be going in the positive y direction. When I changed it to: y(j+1)=y(j)1

the program would freeze. I am really just learning this program and I will be using it throughout my time at college. I would really like to know what I have done and what I need to do just to make the program at least start correctly.

Thank you,

Bruce Headley

Answer 1

[Bruce Headley]

hold on  
%These are the staring points 
x(1)=50; 
y(1)=10;  
dx=1; 
dy=1;
%Direction in which the ball will move right 1 left -1 
x_dir=[-1 1]; 
%Direction in which the ball will move up 1 down -1 
y_dir=[-1 1]; 
xdir=x_dir(randi([1,2],1)); 
ydir=y_dir(randi([1,2],1));

%while y(j)>=10 means game over, the other if statements are meant to bounce the ball off of that line.

j=1;   
  while y(j)>=10; 
       x(j+1)=x(j)+dx*xdir; 
       y(j+1)=y(j)+dy*ydir; 
       if x(j+1)<=70; 
         xdir=-1; 
         ydir=y_dir(randi([1,2],1)); 
     end 
       if x(j+1)>=30; 
         xdir=1; 
         ydir=y_dir(randi([1,2],1)); 
     end 
       if y(j+1)>=110; 
         xdir=x_dir(randi([1,2],1)); 
         ydir=-1; end

        plot(x,y,'bo');
        j=j+1;
    end
    hold off

I just realized that the code was jumbled up so I fixed it to make it easier to read.

Thanks again.

Answer 2

[Walter Roberson]

if j == 1; ydir = 1; end

then continue on with your

y(j+1)=y(j)+dy*ydir;

[Bruce Headley]

I tried adding that statement in between the:

while y(j)>=10;

x(j+1)=x(j)+dx*xdir;

and then in between:

x(j+1)=x(j)+dx*xdir;

y(j+1)=y(j)+dy*ydir;

and I got the same results. Either it starts and stop right then or it goes out of bounds for some reason.

Thank you