how to calculate the loop for variables?

[Fred Lee]

I need to calculate the second row variable minus the first row variable, the fourth row variable minus the third row variable, the sixth row variable minus the fifth row variable
How to write such loop?
Thanks so much!

* Example generated by -dataex-. For more info, type help dataex
clear
input float(var1 var2 v3 v4 variable5 variable6)
1 2 3 5 6 7
end

[Øyvind Snilsberg]

rename * v#, addnumber

forval i=2(2)6 {
local j=`i'-1
gen v`i'_v`j' = v`i' - v`j'
}

[Fred Lee]

Great, thanks so much!