There are several things wrong in your program.
1.
The operation of your 'for' loop is that it assigns to 'j' the values 0 up to N-1 subsequently.
You tear that down by immediately inside the loop assigning 0 to 'j' with 'j<-0'; no matter which run of the 'for' loop you're in, 'j' is always 0 inside. This makes 'k' to be a range from 0,1...Occur 0-1. It is also not necessary to increment ('j<-j+1') at the end of the loop, because that is also implied in the 'for' loop operation. In your case it assigns j+1=0+1=1 to j. So j becomes 1. Always.
2.
The index into an array for assignment must be an integer, cannot be a range. That's why you get an error flagged at the assignment to 'Val k'.
3.
The stack() function is useless when called with a single argument. Stack() wants to stack (at least) two things; 'stack(Val)' just gives 'Val'.
My guess is that you're after something like this:
Success!
Luc
