Can you shoot 380 ACP and 9x18 with the same gun?

NO. The .380 ACP is a 9 x 17 cartridge. The 9x18, also known as the 9mm Makarov, is not truly a 9mm cartridge- it is 9.27mm. The cartridge is too long, too fat, and too powerful to be shot in a .380 ACP pistol.