4/11 arithmeticOp.checkOperands, changed two cstrs in constSTO and STO
4/12 fix constSTO nullptrException
4/12 ready to test error message in DoBinaryOp()
4/12 ready to test error message
Merge remote-tracking branch 'origin/zhu' into david

Conflicts:
	CSE131_PA1/check1.rc
Revert "4/12 ready to test error message"

This reverts commit 6425b2eca1b0368bf894949fe988f1f0fc6a80ef.
4/12 shit happened
parser revert
Merge remote-tracking branch 'origin/david' into zhu
1
useless
useless
try1