Using awk to edit numbers in a column

Question

lets say I have a basic text file that looks like this:

91 N 91 H 1.48
95 N 95 H -0.26
97 N 97 H 1.79
98 N 98 H -0.76

I want to change columns 1 and 3 so that the integer values are n-3 like this:

88 N 88 H 1.48
92 N 92 H -0.26
94 N 94 H 1.79
95 N 95 H -0.76

I realize awk is probably the best way to do this, but i have no idea how to get awk to apply a formula to a column, or for that matter for awk to treat a column as integer values. Is there a simple script that could do this? Also on that note: what a good comprehensive guide to how to use awk, because the ones I've seen so far are just example scripts of how to do things.

Answer 1

This substracts 3 from columns 1 and 3:

$ awk '{$1-=3; $3-=3; print;}' file
88 N 88 H 1.48
92 N 92 H -0.26
94 N 94 H 1.79
95 N 95 H -0.76

-= is the usual subtract-from operator. It works the same in awk as it does in C or python.