USTC 2021 compiler lab2

1. Array declaration: partly done, symbol table entry format DONE ; first dimension missing DONE
2. Array element used in expression: DONE
3. Array element assignment. (as left value): DONE, note: dimension overflow UNDONE, should be done with runtime check, suggest adding a new instruction to check
4. print function: DONE(array element, constant, variable as argument)
5. Array initilization(C style): DONE