Find the first element of a column in a matrix that has a value equal to zero

I have an m by n matrix and I'm interested in the nth column. Initially all of the values in the nth column are greater than zero. As the code executes, at some point, a specific row in the nth column will equal zero. I want to determine which row that is. One issue is that after this first instance of zero, all of the subsequent rows in the nth column will also equal zero. I just want the first row in the last column that has a value of zero.

[Robert Demyanovich]

This answer worked fine. However, now I realize that I need the value of m that matches the value of n found by the answer.

Answer 1

[Dyuman Joshi]

r=find(A(:,n)==0,1)     %A is your m by n matrix after executing the code