matrix manipulations of columns

How can I replace all even columns of matrix A by columns of ones.

pls note that matrix A is A=random('norm',3,0.2,100,100)

thx

Answer 1

[Azzi Abdelmalek]

A=random('norm',3,0.2,100,100)
A(:,2:2:end)=ones(size(A(:,2:2:end)))