Why is this loop not ending?

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Simone Frauenfelder
Simone Frauenfelder on 26 Apr 2017
Commented: Rena Berman on 28 Apr 2017
function [ number ] = SmallestNumber(n,a,b)
% Smallest natural number function
% inputs:
% n = maximum value
% a = first number n should be divisible
% b = second number n should be divisible by
% output:
% number = the smallest number (not exceeding the value of 'n') that is % divisible by 'a' and 'b'
i = 1;
while i =< n
A = rem(i,a);
B = rem(i,b);
if A <= 0 && B <= 0;
number = i
else
i = i + 1;
end
end
This loop is an infinite loop, how can I fix it so it ends and displays 'number = '?
Thank you!
  2 Comments
Stephen23
Stephen23 on 26 Apr 2017
@Simone Frauenfelder: editing your question text away will not encourage people to help you. You unilaterally decide that our volunteer efforts are disposable according to your own wishes, because now our answers are meaningless to anyone else. This will not encourage people to help you, if they know that they will be treated as your own personal consultancy.
Rena Berman
Rena Berman on 28 Apr 2017
(Answers Dev) Restored edit

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Answers (2)

KL
KL on 26 Apr 2017
Edited: KL on 26 Apr 2017
Your loop variable increment i=i+1; is part of the else case so once the condition becomes true, i is not incremented. Move that statement outside and you'll see your result. Something like this
if A <= 0 && B <= 0;
number = i
break;
end
i = i + 1;
end % end from while loop
Adding break after finding the number breaks the loop.

Stephen23
Stephen23 on 26 Apr 2017
Edited: Stephen23 on 26 Apr 2017
It would be simpler to use a for loop, then break is not required:
function num = SmallestNumber(n,a,b)
num = Inf;
for k = n:-1:2
if rem(k,a)==0 && rem(k,b)==0
num = k;
end
end
end
And tested:
>> SmallestNumber(100,9,6)
ans = 18

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