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Hello,

I want to sort numbers in an arrey without using sort function, but with bubblesort (swapping number next each other until all numbers are sorted)

Here is what I have...

X=[10 1 29 89 5 56 76 8];

finished=0;

while finished==0

if finished==0

for i=1:size(X,2)-1

if X(i)>X(i+1)

c=X(i);

X(i)=X(i+1);

X(i+1)=c;

end

end

end

if X(i)<X(i+1) || X(i)==X(i+1)

finished=1;

end

end

disp(X)

I understand that this loop works by comparing numbers next each other (like comparing 10 with 1). Then, if the front number (10) is bigger than the next number (1), the numbers are swaped. However, I want to break the loop once all numbers are sorted from the minimum number to the maximum number.

The code above only sorts the numbers until [1,10,29,5,56,76,8,89], so I want to loop several more to complete the sorting, but I want the code stops when the sorting is done. Otherwise, the code keeps on looping again and again.

I really appreciate if I get some help with this problem.

James Tursa
on 27 Nov 2019

Simply set your "finished" flag depending on whether a swap was done or not. E.g.,

while true

finished = 1;

for i=1:size(X,2)-1

if X(i)>X(i+1)

c=X(i);

X(i)=X(i+1);

X(i+1)=c;

finished = 0;

end

end

if finished

break

end

end

The for-loop can also be shortened by realizing that after each pass you are guaranteed to have one more element sorted at the bottom. I.e., the for-loop doesn't have to examine the entire array each time ... at each iteration you only have to examine one fewer elements.

James Tursa
on 27 Nov 2019

the cyclist
on 27 Nov 2019

In case you were asking something different ... the syntax

if finished

works because when the variable finished takes the value "1", that value will be converted to the boolean "true", and the if statement will be entered. In general, the condition always has to be evaluated to true/false.

I would argue that slightly better programming practice would have been to define the variable finished as a boolean false in the first place. But that's fairly precious. It's more important to get the code to work correctly first, before worrying about such nuances.

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the cyclist
on 27 Nov 2019

Edited: the cyclist
on 27 Nov 2019

if all(diff(X)) >= 0

Also, rather than defining the finished variable, you could have just made that the condition for the while loop:

while not(all(diff(X)) >= 0)

or, mathematically equivalently but a bit more elegantly

while any(diff(X)) < 0

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