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#include <iostream> | |
#include <stack> | |
#include <string> | |
#include <sstream> | |
#include <map> | |
#include <cassert> | |
#include <cstdlib> | |
using namespace std; | |
#define ERR err(__LINE__) | |
map<char, int> priority = { | |
{ '\0', -256 }, | |
{ '(', -1 }, | |
{ ')', -1 }, | |
{ '+', 1 }, | |
{ '-', 1 }, | |
{ '*', 2 }, | |
{ '/', 2 }, | |
}; | |
stack<char> op; | |
stack<double> num; | |
void err(int line) { | |
cout << "error at line " << line << endl; | |
assert(0); | |
} | |
double popNum() { | |
double a = num.top(); | |
num.pop(); | |
return a; | |
} | |
void popOp() { | |
char c = op.top(); | |
if(c == '\0') | |
ERR; | |
if(c != '(') { | |
cout << c << ' '; | |
double b = popNum(); | |
double a = popNum(); | |
if(c == '+') { num.push(a+b); } | |
if(c == '-') { num.push(a-b); } | |
if(c == '*') { num.push(a*b); } | |
if(c == '/') { num.push(a/b); } | |
} | |
op.pop(); | |
} | |
int main() { | |
cout << '>'; | |
op.push('\0'); | |
while(true) { | |
string input; | |
cin >> input; | |
if(input == "end") { | |
while(op.top() != '\0') | |
popOp(); | |
break; | |
} | |
if(isdigit(input[0])) { | |
num.push(atof(input.c_str())); | |
cout << num.top() << ' '; | |
} | |
else { | |
char c = input[0]; | |
if(c == '(') { | |
op.push(c); | |
} | |
else if(c == ')') { | |
if(op.top() == '(') | |
ERR; | |
while(op.top() != '(') | |
popOp(); | |
popOp(); | |
} | |
else { | |
while(priority[c] <= priority[op.top()]) | |
popOp(); | |
op.push(c); | |
} | |
} | |
} | |
cout << endl << num.top() << endl; | |
} |
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