表达式计算

 1 stack<char> ops;
 2 stack<int> nums;
 3 ops.push(‘#‘);
 4 
 5 for (; ops.top() != ‘#‘ || (current != ‘#‘); current = readNext()) {
 6     if (!isOperator(current)) {
 7         nums.push(current);
 8     } else if (current > ops.top()) {
 9         ops.push(current);
10     } else if (current == ops.top()) { // if "()"
11         ops.pop();
12     } else {
13         int n1 = nums.top(); nums.pop();
14         int n2 = nums.top(); nums.pop();
15         nums.push(operate(n1, n2, ops.top());
16         ops.pop();
17     }
18 }
19 
20 return nums.top();