# to just iterate over an array; each element assigned to $_
# changing $_ changes the original array element

for (@array) {
    # assigning to $_ here will change original array
    # comparing to $_ of course will not
}

# to iterate over a range
for (0..10) {
    # $_ will be set to 0 to 10 in sequence
}

# to iterate over a range with a named op
for $i(0..10) {
    # $i will be set to 0 to 10 in sequence
}