# Change for-loop iteration inside the loop.

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M G on 10 Oct 2013
Answered: Hector Cano on 14 Feb 2020
Dear Matlab users,
I would like to change the For-loop iteration inside the loop if a condition is met. Suppose:
for i = 1:500
pause(0.1)
display(i)
if i == 40
i = 300;
end
end
So, I want whenever i == 40, the iteration changes from 39 to 300 and continues till 500. The code above does not work and every time the loop resets the i value. What I want should look like this:
i = 1, 2, 3, ... 39, 300, 301, 302, 303, ... 500.

#### 1 Comment

Himanshu Nagpal on 14 Jun 2016
You can use the following code
i = 1;
while (i <= 500)
pause(0.1)
display(i)
i = i + 1;
if (i == 40)
i = 300;
end
end

Roger Stafford on 10 Oct 2013
Edited: Roger Stafford on 10 Oct 2013
Matlab's for-loop is designed so that you cannot change its index, in this case, 'i', within the loop. Even though you have set it to 300, it will stubbornly return on the next trip with i = 41, not 300. To do what you indicate here you should do this instead:
for i = [1:39,300:500]
pause, etc ...
end
If a change in indexing cannot be predicted in advance of entering a for-loop you should use the 'while-end' construct instead where you must control the index yourself instead of an automatic advance at each step. Either that or if you want to sudden depart ahead of time from a for-loop, use the 'break' function.

M G on 10 Oct 2013
Hi Roger, Thanks for response, but what if the IF-statement varies every time?
Roger Stafford on 10 Oct 2013
See the edited version of my answer.

Sachin Patil on 20 Sep 2016
i = 1;
for j = 1:500
pause(0.1)
display(i)
i = i + 1;
if i == 40
i = 300;
end
end

Hector Cano on 14 Feb 2020
clc;clear;close all
n=[1 1 100];
while (n(1) <= n(3))
j(n(1))=n(1);
if (n(1) == 50)
n(2) = 10;
end
n(1) = n(1) + n(2);
if (n(1)==n(3))
n(3)=200;
end
end
j(j==0)=nan;
plot(j,'*-r')