Replacing zeros with other values

A=[1 2 3 4;
   4 5 0 0;
   1 0 0 1;
   0 1 1 1]

I want to replace zeros in the third column with last known values. The result should be

    A=[1 2 3 4;
       4 5 3 0;
       1 0 3 1;
       0 1 1 1]
 What should be the code.

Answer 1

[KSSV]

A3=A(:,3);
A3(A3==0)=3;
A(:,3)=A3;

[Mido]

Thanks for your answer but what if it is a long column with other zeros I want the code to detect the known number before each zero and then replaces the zero with this number.

[Mido]

while any(A(:)==0)
  ii1=A==0;
  ii2=circshift(ii1,[-1 0]);
  A(ii1)=A(ii2);
end

I found this code in this forum but it solves the problem for all columns andI want it for the third column only.

[KSSV]

Make A as A3 and run it. Replace the column in A.

[Mido]

Brilliant! Thank you very much.

[Mido]

I have one more question. If I have a matrix like this

A= [1 1; 
    1 2; 
    1 3; 
    1 4;
    2 1; 
    2 2; 
    2 3;
    2 4]

I want to extract rows from the matrix as follows: For each different number in the first column extract rows using increment of 2 in the second column. The result will be:

A=   [1 2; 
      1 4; 
      2 2; 
      2 4]

[KSSV]

A(2:2:end,:)