The building of one of the softwares I am installing is failing because of the error

c++: internal compiler error: Killed (program cc1plus)

I think this is because I have only 500Mb swap partition. So I am trying to increase it using an external pendrive. I have tried adding

/dev/sdb1 none swap sw 0 0

/dev/sdc1 none swap sw 0 0

( since on booting, sometimes the pendrive partition shows /dev/sdb1 while sometimes it shows /dev/sdc1) to the /etc/fstab file but still instead of showing System as Linux swap on using

fdisk -l

it is showing FAT16. I have also tried

mkfs.ext3 /dev/sdb1

so that we create swap on a linux type filesystem,
but it says:

/dev/sdb1 is mounted; will not make a filesystem here!

I also tried

sudo swapon /dev/sdb1

but I get

swapon: /dev/sdb1: read swap header failed: Invalid argument

Please guide me so that I can make a swap partition on my pendrive.

PS: I have root permission.