Simple integer operation calculator
Python 2, 48 bytes

i=0
for c in input():exec"i=i%s2&amp;-2"%c
print i/2


Does +2, -2, *2, or /2. By doing +2 and -2 rather than +1 and -1, we're working in doubled units, so the final output needs to be halved. Except, the floor-division / now needs to round down to a multiple of 2, which is done with &amp;-2.