How to separate matrix row?

let's say

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

A =

     1     2
     1     2
     1     2

Any command that can I separate it into turn into

 B =
     1     2
     1     2
     1     2

 C = 
     0   2
     0   2
     0   2

Thanks!!

-------------- I try to do it like this, but doesn't work

 B = A(:,1)

B =

     1
     1
     1

[Wayne King]

you dramatically changed what you wanted from this post in just a few minutes, so I'm not sure exactly what result you want now.

Answer 1

[Thomas]

use

A =[1     2
     1     2
     1     2]
 A(:,1)=0;
 B=A

[chewkaisheng]

Thank you!!

It's really work!

Actually my matrix is about the sound signal..

although it become zeros , but still have a little of signal listening...

Answer 2

[Wayne King]

   A = [ 1 2; 1 2; 1 2];
   A(:,1) = zeros(size(A,1),1);

Or if you want to keep your original A

    B = zeros(size(A));
    B(:,2) = A(:,2);