i want the loop to run only one time, it keeps running until it subtract 84 instead of 6

clc, close all, clear all
A=[75 144 114 102 108; 90 126 102 84 126; 96 114 75 105 135; 105 90 150 90 75; 90 75 135 75 90; 105 60 165 45 120; 115 85 160 100 145];
num_rows= length(A)
num_columns= width(A)
for i=1:num_rows
    for j=1:num_columns
        if A(:,4)
            A(:,4) = A(:,4) - 6
        end
    end
end

Answer 1

[Jan]

Remember that length(A) replies the longest dimension. Maybe you meant height(A). Even if this replies the same value for the example data, avoid length, because it can fail easily.

if A(:,4) might not do, what you expect. The if command requires a scalar condition. A(:,4) is a vector. Therefore Matlab inserts an all() implicitly. Is this wanted?

You run a loop over rows and columns of A, but process A(:,4) only. The body of the loops does not depend on i or j, so what is the purpose of the loops? Most of all, if you want to run the loop once only - isn't it the direct way to omit the loop?

[batool swaeer]

You run a loop over rows and columns of A, but process A(:,4) only. The body of the loops does not depend on i or j, so what is the purpose of the loops?

I know I could solve this issue by just creating another matrix (zeros and 6) and subtracting it from the ooriginal matrix. However, my instroctur wants it to be a loop.

and changing it to Length still gave the same outcome.

[Jan]

@batool swaeer: I do not understand, what "creating another matrix (zeros and 6)" means. What does "it" mean in "changing it to Length"?

Did you get the core of my answer?

for i=1:num_rows                   % Loop over rows
    for j=1:num_columns            % Loop over columns
        if A(:,4)                  % \
            A(:,4) = A(:,4) - 6    %  | does not depend on i or j
        end                        % /
    end
end

A shorter version of this code:

A(:, 4) = A(:, 4) - 6 * (num_rows * num_cols)

It is still not clear what "run the loop only one time" means. This is a contradiction to the nature of loops.