后缀表达式实现表达式求值

看到别人写的一个表达式求值程序，想到很久之前写的一个。中间有个字符串转数值型，可以用stringstream来实现或者c语言里面的strtod直接得到

#include<iostream>#include<string>#include<cmath>#include<stack>#include<vector>using namespace std;class Data{public:double value;bool is_fuhao;int priority;char fuhao;Data():is_fuhao(false){}};double get_value(string str){if(str.length()==1)return (int)str[0]-(int)'0';int int_part=0;double doub_part=0;string::size_type i=0;for(;i<str.length()&&str[i]!='.';++i)int_part=10*int_part+(int)str[i]-(int)'0';if(i!=str.length()){string s1(str,i+1,str.length()-i-1);double m=get_value(s1);doub_part=m/pow(10.0,(int)s1.length());}return int_part+doub_part;}int main(){string s;while(cin>>s){vector<Data> vdata;vector<Data> hou_zui;stack<Data> temp_stack;stack<double> result;for(string::size_type i=0;i!=s.length();){Data m_data;if(s[i]=='+'||s[i]=='-'||s[i]=='*'||s[i]=='/'||s[i]=='('||s[i]==')'){m_data.is_fuhao=true;m_data.fuhao=s[i];if(s[i]=='+'||s[i]=='-')m_data.priority=1;else if(s[i]=='('||s[i]==')')m_data.priority=0;elsem_data.priority=2;++i;}else{string::size_type flag=i,len=1;++i;if(i!=s.length()){while(s[i]!='+'&&s[i]!='-'&&s[i]!='*'&&s[i]!='/'&&s[i]!='('&&s[i]!=')'){++len;++i;if(i==s.length())break;}string s_temp(s,flag,len);m_data.value=get_value(s_temp);}elsem_data.value=s[flag]-'0';}vdata.push_back(m_data);}bool flag=true;for(vector<Data>::iterator i=vdata.begin();i!=vdata.end();++i){if(!i->is_fuhao)//如果不是符号hou_zui.push_back(*i);else{if(temp_stack.empty()||i->fuhao=='(')temp_stack.push(*i);else{if(i->priority<=temp_stack.top().priority&&i->fuhao!=')'){while(temp_stack.top().priority>=i->priority){hou_zui.push_back(temp_stack.top());//cout<<temp_stack.top().fuhao<<endl;temp_stack.pop();if(temp_stack.empty())break;}temp_stack.push(*i);}else if(i->fuhao==')'){while(temp_stack.top().fuhao!='('){hou_zui.push_back(temp_stack.top());temp_stack.pop();}temp_stack.pop();}else{temp_stack.push(*i);}}}}while(!temp_stack.empty()){hou_zui.push_back(temp_stack.top());temp_stack.pop();}for(vector<Data>::iterator i=hou_zui.begin();i!=hou_zui.end();++i){if(!i->is_fuhao)result.push(i->value);else{if(i->fuhao=='+'){double a,b;a=result.top();result.pop();b=result.top();result.pop();result.push(b+a);}else if(i->fuhao=='-'){double a,b;a=result.top();result.pop();b=result.top();result.pop();result.push(b-a);}else if(i->fuhao=='*'){double a,b;a=result.top();result.pop();b=result.top();result.pop();result.push(b*a);}else{double a,b;a=result.top();result.pop();b=result.top();result.pop();result.push(b/a);}}}cout<<result.top()<<endl;}return 0;}