# How to end loop after key is press

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Addison Collins on 15 Jul 2021
Edited: Addison Collins on 15 Jul 2021
Hello everyone,
I am attempting to make it so I can have as many iterations as I want in the for loop. I want to choose when I am done using ginput rather than relying on a preset number ("num" in the code below). This would mean running the loop until I press a key, after which the loop is exited. I have attached an image of the plot.
EDIT: I edited the code posted below to reflect my final script that works. If enter is pressed, ginput will not throw an error, and the loop will be exited. If another key is pressed, the loop will also stop. NOTE that when a different key other than 'ENTER' is used to break from the loop, an additional point will be plotted wherever the cursor is located. I am too lazy to fix this at the moment.
clc;clear;close all
rng default
xq = rand(500,1)*5;
yq = rand(500,1)*5;
f = figure;
j = 1;
plot(xq,yq,'b+'); hold on;
axis equal
while true
try % ginput(number) throws error when 'ENTER' is pressed
[xv(j), yv(j)] = ginput(1);
plot(xv(j),yv(j),'ro','MarkerFaceColor','r','MarkerSize',3)
if j > 1
plot(xv(j-1:j),yv(j-1:j),'LineWidth',2,'color','red') % polygon
end
j=j+1;
catch
break;
end
% In case something other than enter is pressed
if f.CurrentCharacter > 0
break;
end
end
in = inpolygon(xq,yq,xv,yv);
figure
plot(xv,yv,'LineWidth',2,'color','red') % polygon
axis equal
hold on
plot(xq(in),yq(in),'r+') % points inside
plot(xq(~in),yq(~in),'bo') % points outside
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### Accepted Answer

Scott MacKenzie on 15 Jul 2021
Edited: Scott MacKenzie on 15 Jul 2021
Here's an arrangement I've used with good success in the past. The loop executes indefinitely until a key is pressed.
f = figure;
% other code
while true
% put your loop code here
if f.CurrentCharacter > 0
break;
end
end
##### 5 CommentsShow 3 older commentsHide 3 older comments
Scott MacKenzie on 15 Jul 2021
Edited: Scott MacKenzie on 15 Jul 2021
I've deleted this comment, as I see in your next comment that you've now got things working just fine.
Addison Collins on 15 Jul 2021
I realized that ginput just doesn't like 'ENTER'. It attempts to return an invalid 0x0 or something along those lines. Instead, if I press any other key, it works (spacebar, etc.). Additionally, I added a catch so if enter is pressed it will break rather than throw an error.
I will edit my orignal post for anyone who sees this thread in the future.
clc;clear;close all
rng default
xq = rand(500,1)*5;
yq = rand(500,1)*5;
f = figure;
j = 1;
plot(xq,yq,'b+'); hold on;
axis equal
while true
try % ginput(number) throws error when 'ENTER' is pressed
[xv(j), yv(j)] = ginput(1);
plot(xv(j),yv(j),'ro','MarkerFaceColor','r','MarkerSize',3)
if j > 1
plot(xv(j-1:j),yv(j-1:j),'LineWidth',2,'color','red') % polygon
end
j=j+1;
catch
break;
end
% In case something other than enter is pressed
if f.CurrentCharacter > 0
break;
end
end
in = inpolygon(xq,yq,xv,yv);
figure
plot(xv,yv,'LineWidth',2,'color','red') % polygon
axis equal
hold on
plot(xq(in),yq(in),'r+') % points inside
plot(xq(~in),yq(~in),'bo') % points outside

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