Question regarding loops

Question

For ( j=1 ; j < n ; j + = )
In this loop what does j + = mean ?

Answer 1

Addition assignment

for (j=1 ; j < n; j += i) // the value "i" will be added to the current value "j" for each loop until the value "j" becomes "n"

Answer 2

j += is incomplete statement.
In addition to explained j += i,

If You may mean j++; then j value incremented by 1. It is short of j += 1. And j += i is short form of j = j + i ;