#include<iostream>
#include<stdio.h>
#include<string>
#include<stack>
#include<queue>
#include<map>
using namespace std;
struct node{
double num;
char op;
bool flag;
};
string str;
stack<node> s;
queue<node> q;
map<char,int> op;
void Change()
{
// 中缀转后缀
node temp;
for(int i = 0; i < str.length();)
{
if(str[i] >= '0' && str[i] <= '9')
{
// 处理数字
temp.flag = true;
temp.num = str[i++] - '0';
while(i < str.length() && str[i] >= '0' && str[i] <= '9')
{
temp.num = temp.num * 10 + str[i] - '0';
i++;
}
q.push(temp);
}
else{
// 处理操作符
temp.flag = false;
while(!s.empty() && op[str[i]] <= op[s.top().op])
{
q.push(s.top());
s.pop();
}
temp.op = str[i];
s.push(temp);
i++;
}
}
while(!s.empty())
{
q.push(s.top());
s.pop();
}
}
double Cal()
{
// 计算后缀表达式的值
double temp1, temp2;
node cur, temp;
while(!q.empty())
{
cur = q.front();
q.pop();
if(cur.flag == true) s.push(cur);
else{
temp2 = s.top().num;
s.pop();
temp1 = s.top().num;
s.pop();
temp.flag = true;
if(cur.op == '+') temp.num = temp1 + temp2;
else if(cur.op == '-') temp.num = temp1 - temp2;
else if(cur.op == '*') temp.num = temp1 * temp2;
else temp.num = temp1 / temp2;
s.push(temp);
}
}
return s.top().num;
}
int main()
{
op['+'] = 1;
op['-'] = 1;
op['*'] = 2;
op['/'] = 2;
getline(cin,str);
for(string::iterator it = str.end(); it != str.begin(); it--)
{
if(*it == ' ') str.erase(it);
}
while(!s.empty()) s.pop();
Change();
printf("%.2f\n", Cal());
return 0;
}
栈与队列的应用——计算表达式的值
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转载自blog.csdn.net/tian__si/article/details/113861057
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