中缀表达式转后缀表达式并计算相应的值
注意：值可能为小数
#include <iostream>
#include <cstdlib>
#include <string>
#include <cstring>
#include <map>
#include <stack>
#include <queue>
using namespace std;
double cal(queue<string> su){
stack<double> nums;
while(!su.empty()){
if('0' <= su.front()[0] && su.front()[0] <= '9'){
//数字字符串转换
char ch[20];
strcpy(ch, su.front().data());//char数组可直接给string类型赋值，反之不行，可以使用strcpy()函数结合string类型的data()方法
//char ch[20] = "2.34";
nums.push(atof(ch));//atof()字符串转换浮点型数字 ，相应的还有atoi(),atol(),在<cstdlib>中
cout<<"进栈："<<atof(ch)<<endl;
su.pop();
}else{
//注意两个操作数的赋值是倒过来的
double b = nums.top();
nums.pop();
double a = nums.top();
nums.pop();
char c = su.front()[0];
if(c == '+'){
nums.push(a + b);
cout<<"进栈："<<a + b<<endl;
}else if(c == '-'){
nums.push(a - b);
cout<<"进栈："<<a - b<<endl;
}else if(c == '*'){
nums.push(a * b);
cout<<"进栈："<<a * b<<endl;
}else{
nums.push(a / b);
cout<<"进栈："<<a / b<<endl;
}
su.pop();
}
}
return nums.top();
}
int main(int argc, char *argv[]) {
map<char, int> m;
m['+'] = 0;
m['-'] = 0;
m['*'] = 1;
m['/'] = 1;
string str;
stack<char> s;
queue<string> suffix;
int i;
string temp;
while(cin>>str){
for(i = 0; i < str.size(); ++i){
if('0' <= str[i] && str[i] <= '9'){
temp = "";
while(('0' <= str[i] && str[i] <= '9') || str[i] == '.'){
//截取数字
temp += str[i];
++i;
}
--i;//注意
cout<<temp<<" ";
suffix.push(temp);
}else if(s.size() == 0 || str[i] == '('){
s.push(str[i]);
}else if(str[i] == ')'){
temp = "a";//将单个字符转换成字符串：
//法一：定义一个长度为1的字符串，然后直接替换第一个位置
//法二：将字符赋值给字符数组，char ch[2] = {c,0},第二个0为字符串结束符\0,再将字符数组赋值给字符串
//注意不能使用："" + c;
while(!s.empty() && s.top() != '('){
//注意
temp[0] = s.top();
cout<<temp<<" ";
suffix.push(temp);
s.pop();
}
s.pop();//左括号舍弃
}else{
if(m[str[i]] > m[s.top()] || s.top() == '('){
s.push(str[i]);
}else{
temp = "a";
while(!s.empty() && m[str[i]] <= m[s.top()]){
temp[0] = s.top();
cout<<temp<<" ";
suffix.push(temp);
s.pop();
}
s.push(str[i]);//注意，第一遍忘了放
}
}
}
temp = "a";
while(!s.empty()){
temp[0] = s.top();
cout<<temp<<" ";
suffix.push(temp);
s.pop();
}
cout<<endl;
double re = cal(suffix);
cout<<"结果是：";
cout<<re<<endl;
}
return 0;
}