How to use inputdlg with plotting a bouncing ball?

I am trying to write a script that shows a ball bouncing around in a figure window. I have done it without using the inputdlg with this script...

clear; clc; close all;
figure(1); grid on; hold on; axis equal
axis([0 15 0 10])

xlast = 5; % initial location
ylast = 7.5; % initial location
ulast = -20; % u is our initial vertical velocity
delX = 0.01; % initial horizontal velocity
delT = 0.01; % time step

% system constants
g = -15.81;

% plot the current location of the ball
for ii = 2 : 10000; 
    unow = g*delT + ulast;
    ynow  = ulast*delT + ylast;
    xnow = xlast + delX;
    if ynow <= 0.0
        unow = (-0.94)*unow;
        ynow = 0.0;
    end
    if xnow >= 15
        delX = (-0.94)*delX;
        xnow = 15.0;
    end
    if xnow <= 0
        delX = (-0.94)*delX;
        xnow = 0.0;
    end
    delete(findobj('tag','delete me'));
    plot(xnow, ynow, 'go', 'linewidth', 2, 'tag', 'delete me');
    drawnow;
    ulast = unow; xlast = xnow; ylast = ynow;
end

But I need to include the inputdlg function now and it keeps showing me an error in the plot command about vectors needing to be the same length. I think they are...

clear; clc; close all;
figure(1); grid on; hold on; axis equal
axis([0 12 0 12])
delT = 0.01; % time step

% system constants
g = -15.81;

prompt={'Ball1 initial X loc', 'Ball2 initial Y loc', 'Ball1 intial Y velocity', 'Ball1 initial X velocity'};
name='Initial Values';
numlines=1;
defaultanswer={'5','7.5','-20','0.01'};

output_values=inputdlg(prompt,name,numlines,defaultanswer);

for ii = 2 : 10000;
    unow = g*delT + str2num(output_values{3});
    ynow  = (str2num(output_values{3}))*delT + str2num(output_values{2});
    xnow = str2num(output_values{1}) + str2num(output_values{4});
    if ynow <= 0.0
        unow = (-0.94)*unow;
        ynow = 0.0;
    end
    if xnow >= 12
        delX = (-0.94)*str2num({4});
        xnow = 12.0;
    end
    if xnow <= 0
        delX = (-0.94)*str2num({4});
        xnow = 0.0;
    end
    delete(findobj('tag','delete me'));
    plot(xnow, ynow, 'go', 'linewidth', 2, 'tag', 'delete me');
    drawnow;
    str2num(output_values{3}) = unow; str2num(output_values{1}) = xnow; str2num(output_values{2}) = ynow;
end

Please help me figure out how to keep this same concept and include the use of the inputdlg box.

Answer 1

[Andrew Schenk]

There are some syntax errors in the second version of your code. For example,

 delX = (-0.94)*str2num({4});

should instead be

 delX = (-0.94)*str2num(output_values{4});

A better approach instead having to rewrite all of your MATLAB code using the output_values variable is to use the first version of your code and modify it so the variables are assigned from the inputdlg result as shown below:

 prompt={'Ball1 initial X loc', 'Ball2 initial Y loc', 'Ball1 intial Y velocity', 'Ball1 initial X velocity'};
name='Initial Values';
numlines=1;
defaultanswer={'5','7.5','-20','0.01'};
output_values=inputdlg(prompt,name,numlines,defaultanswer);
xlast = str2num(output_values{1});
ylast = str2num(output_values{2});
ulast = str2num(output_values{3});
delX = str2num(output_values{4});