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# Hello can somebody tell me what I am doing wrong?

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D'Monte Pittman on 16 Jul 2015
Closed: MATLAB Answer Bot on 20 Aug 2021
I am trying to write a MATLAB program using a forloop to determine the number of values that are positive, negative, and the number of values that equal zero in a vector containing 'N' elements. I can't get it to work.
format compact
v = input('Enter the number of elements in the Vector: ');
a = input('Enter the Array:');
for i = 1:length(a)
if v > 0
fprintf('v>0',i)
elseif v < 0
fprintf('v<0',i)
else
fprintf('v=0',i)
end
end

Jos (10584) on 16 Jul 2015
This is a working for-loop, which prints out something that resembles your goal:
a = input('Enter the Array:');
for i = 1:length(a)
v = a(i) ; % get the i-th element of a
if v > 0
fprintf('v>0',i)
elseif v < 0
fprintf('v<0',i)
else
fprintf('v=0',i)
end
end
However, the next step is to learn to do this in a matlab-like way
V = input('Enter the Array:');
disp('V < 0') ;
idx = find(V<0) ; % all at once
disp(idx) ;

Muthu Annamalai on 16 Jul 2015
Hi Pittman,
In addition to the answer by Jos, I have some observations for you:
1. Enter the data at your runtime as '5', and '[1,2,3,4,5]' (not including the quotes ofcourse)
2. When you use fprintf see MATLAB documentation , you want code like,
fprintf('v < 0 : %d',i);
Ofcourse your code is written in a more C-like fashion, whereas using MATLAB we like to vectorize operations since matrices are native types.
HTH.