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break command

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etcann
etcann on 3 Nov 2011
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.

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Answers (2)

Christopher Kanan
Christopher Kanan on 3 Nov 2011
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;

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Fangjun Jiang
Fangjun Jiang on 3 Nov 2011
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.

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Jan
Jan on 3 Nov 2011
@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.

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