How can I use while loops to determine if an element is larger than the element below it and store the results in a vector with 1 representing true and 0 representing false?

I coded for my while loop but I can't get the final answer and the error showed that 'Array indices must be positive integers or logical values.' Can someone help me with this? Thank you so much!!

A=randi([0 9],1,randi([100 300]))'
n=numel(A)-1
B=zeros(n,1)
while i<=n
    if A(i)>A(i+1)
        B(i,1)=true
    else
        B(i,1)=false
    end
    i=i+1   
end

[Stephen23]

You are using i as an index. What is the value of i ? (hint: the square root of -1)

Answer 1

[Matt J]

A=randi([0 9],1,10)';
n=numel(A)-1;
B=zeros(n,1);
i=1;
while i<=n
    if A(i)>A(i+1)
        B(i,1)=true;
    else
        B(i,1)=false;
    end
    i=i+1;
end

A.',B.'

ans = 1×10

0 2 1 8 0 9 4 2 6 2

ans = 1×9

0 1 0 1 0 1 1 0 1

Answer 2

[John D'Errico]

"While" this does not answer your question, I would not use a while loop at all. Learn to use MATLAB as it is designed.

A = randn(1,8) % some random numbers

A = 1×8

-0.2087 0.3007 -0.3599 -0.0566 0.4045 -3.0370 -0.3818 0.8694

B = [false,diff(A)>0] % A vector of the same length as A, true when A(i+1) > A(i)

B = 1×8 logical array
   0   1   0   1   1   0   1   1

B is the same length as A. Note that A(1) will never be greater than the preceding element, since there is no preceding element.

Could you use a while loop? Yes. A for loop would make more sense as a loop here, since you want to test EVERY pair of elements.

B = false(size(A)); % preallocate B
for ind = 2:numel(A)
  B(ind) = A(ind) > A(ind-1);
end

B

B = 1×8 logical array
   0   1   0   1   1   0   1   1

Same result as the single statement, but a loop.

CAN you use a while loop? Well, yes. Learn when to use one type of loop over another when you REALLY need to use a loop. A while loop is good when you don't know how often the loop will run. A for loop is right when you have a known, fixed number of iterations.