Position in matrix without using findall

Hello people,
I need help. I don’t know how to find position of non-zero elements in matrix , but without using findall.
I know only with findall.:joy:

XY: What’s wrong with findall?

You can write a loop to solve this problem, looking at each position of the matrix and checking whether it’s zero or not, saving each index where the comparison is false.

If this is for a course, be sure to check with your lecturer/professor whether external help is allowed.