Stack-base machine is a kind of cpu design architecture which sometimes be compared with register-based machine. Unlike register-based machine which used 3 address code taking 1 opcode and 2 corresponding operand e.g. add %eax, 3, stack based machine was designed with opcode with one or zero operand and one long stack which served as registers to take temporary value in calculation.
In this problem, you will be given a program for stack-based machine. You need to write a yacc program to check if the format of the program and evaluate its result.
| Instruction | Description |
|---|---|
| add, sub, mul, mod | Pop 2 operands from stack, perform addition, subtraction, multiplication and modulation and push back the result. |
| inc, dec | Pop 1 operand from stack increase/decrease operand by 1, then push back the result. |
| load | Push a constant on the top of the stack. |
| copy | Copy a constant from stack top, then push it back. |
| delete | Delete 1 operand from stack. |
| switch | Pop 2 operands from stack, switch the order of them, and then push them back to the stack. |
Sample Input 1:
load 1
load 2
sub
load 5
mod
Sample Output 1:
0
Explanation 1:
5 % (2-1) = 0
Sample Input 2:
load 3
load 4
inc
inc
Sample Output 2:
Invalid format
Explanation 2:
If after finish the program, there
are more than 1 numbers in the
stack it will be consider invalid.
Sample Input 3:
load 1
load 1
add
sub
Sample Output 3:
Invalid format
Explanation 3:
No enough operands in stack to perform sub.
Sample Input 4:
load 1
inc
inc
dec
load 3
inc
inc
mul
load 4
dec
dec
mul
inc
Sample Output 4:
21
$ bash script.sh run compiling script
$ ./a.out < [files] cxecute code in [files]