Using `awk`:

`awk -F',' '{ p[NR] = $1;net[NR] = $2+$3-$4} END {for (i=2;i<=NR;i++) print (i-1), p[i], "net = ", net[i]}' data.csv`

Because this is a `csv` file, `FS = ','` or `-F ','`

Next `p` and `net` arrays created. These are indexed on NR(record numbers).

Then a for loop `(i-1), p[i], "net = ", net[i]` works as you planned.
`for` loop is being started from 2 because first line is header line. 

`pipe` in this case is useless use. Anohter thing your loop is good but limit should be `NR` not `NF`.