Change for-loop iteration inside the loop.

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.

[Himanshu Nagpal]

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

Answer 1

[Roger Stafford]

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]

Hi Roger, Thanks for response, but what if the IF-statement varies every time?

[Roger Stafford]

See the edited version of my answer.

Answer 2

[Sachin Patil]

Please see this code

i = 1;

for j = 1:500

pause(0.1)

display(i)

i = i + 1;

if i == 40

     i = 300;

end

end

Answer 3

[Hector Cano]

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')