for loop question, how to put the for loop answer in new matrix

Dear all, I got some problems with my code. I suppose it is basic. However, I can't find where is the problem. I want to find a position in my matrix. First, I would like to find out the number>=9 positions for each column. When I get the position, I would like to get the nearest one and the far one. And I use k=x1-x2, so I can get the distances for each column. if none of the numbers can fit into the statement( x1-x2 empty vector), then skip. In the end, I want to put the information into a new matrix called 'final'. Thank you for your help!

A = [88,2,77,4,5;6,2,9,5,0;6,7,3,4,5;6,7,8,5,6;7,8,9,10,6;7,8,9,99,15;45,55,2,2,2;67,66,56,87,1];

for j = 1:size(A)
    line=A(j,:);
    C=find(line>=9);
    
    x1=max(C);
    x2=min(C);
    
    k=x1-x2   
    
    final(j,:)=k
end

Answer 1

[dpb]

A number of issues with the above code --

1. Don't use line as a variable, it's a builtin important plotting function,
2. size(A) returns a 2-vector, iterating over it is not what you want here, you want only number of columns in A
3. While not fatal, you didn't preallocate the output array final which is inefficient altho for such small array won't be noticeable.

Try something more like

nC=size(A,2);                   % number columns in A
magicNo=9;                      % make variable; don't bury in code so can change easily
res=nan(nC,1);                  % output vector preallocation
for c=1:nC                      % iterate over columns
  C=find(A(:,c)>=magicNo);      % get vector of locations
  if isempty(C), continue, end  % skip if none found, leaves output NaN
  res(c)=range(C);              % save the range of found locations
end

[tengteng QQ]

Sorry for replying late. I really appreciate your help.

Though, may I ask you how can I begin to learn coding in Matlab. I am a real beginner and seems my coding is not appropriate? (like it is not a good idea in your view). And I am feeling so struggle when I have an idea but it is not connected with my coding skill.