break command

Hello,

I have a question in break command.

a=zeros(30,1);
a(1)=1;
for i=1:29
    a(i+1)=a(i)+1;
    if a(i)>20
        break
    end
end
a

And I got a result of a'=[1 2 ... 22 0 0 0 ...0] Well, I wanted it looked like a'=[1 2 ... 20 0 0 0 ...0]

What's wrong with my code? Thanks a lot in advance.

Answer 1

[Christopher Kanan]

I assume you want this:

a=zeros(30,1); 
a(1)=1; 
for i=1:29 
a(i+1)=a(i)+1; 
if a(i+1)>=20 
   break; 
end; 
end; 
a

 However, if you just want the first 20 elements to be 1:20, then you could just do, a = zeros(30, 1);a(1:20) = 1:20;

Answer 2

[Fangjun Jiang]

You can figure it out by going through the for-loop in your brain. The first time that a(i)>20 is satisfied is when a(i)==21, right? Because even if a(i)==20, it won't satisfy a(i)>20. By that time, you've already had a(i+1)=a(i)+1. No wonder that last non-zero value is 22. The code is doing exactly what you tell it to do.

[Jan]

@etcann: Instead of the brain, you can use the debugger also: Set a breakpoint in your code and step through the execution line by line. Then you will see, that "a(i)>20" triggers at i==21 and therefore "a(21+1)" has been set to 22 already.