How to locate the first negative number?

%Amount of user numbers
n=input('Amount of user: ');
D=randn(n,1);  %Random numbers
disp('Random numbers generated:');
disp(D);
i=1:1:n;
l=0;
while D(i,1)>0
    l=l+1;
end
if l>n
        l=('Não existe');
    else
        l=l+1; 
end
disp('the first negative number is:');
disp(l);

Where is the error? Thanks!

Answer 1

[Guillaume]

Use find to locate something in an array:

l = find(D < 0, 1);

If you want to use a while loop, it should be:

%no need for index i, which you never increased anyway
l = 1; %can't index at 0
while l <= n && D(l) > 0 %order of comparison is important to prevent D(l) being evaluated when l >n 
   l = l+1;
end

[Guillaume]

Also note that your original

while D(i) > 0

when i is 1:numel(D), will only be true when all elements of D are positive. In which case, your loop will run forever.

Answer 2

[Rômulo Prazeres]

Thank you so much. =D