C++表达式计算

又是给某人写的作业…

#include <iostream>
#include <stack>
#include <map>
#include <list>
#include <stack>
#include <math.h>
#include <iterator>
using namespace std;
//栈内优先级
map<string,int> isp;
//入栈优先级
map<string,int> icp;
//分离表达式
list<string> Tokenize(const string& str,const string& delimiters){
    list<string> tokens;
    string::size_type delimPos = 0, tokenPos = 0, pos = 0;
    if(str.length()<1)  return tokens;
    while(1){
        delimPos = str.find_first_of(delimiters, pos);
        tokenPos = str.find_first_not_of(delimiters, pos);
        if(string::npos != delimPos){
            if(string::npos != tokenPos){
                if(tokenPos<delimPos){
                    tokens.push_back(str.substr(pos,delimPos-pos));
                }else{
                    tokens.push_back("");
                }
            }else{
                tokens.push_back("");
            }
            pos = delimPos+1;
        } else {
            if(string::npos != tokenPos){
                tokens.push_back(str.substr(pos));
            } else {
                tokens.push_back("");
            }
            break;
        }
    }
    return tokens;
}
inline bool isNumber(char c){
    return c=='.'||'0'<=c&&c<='9';
}
inline bool isSymbol(string op) {
	return op=="+"||op=="-"||op=="*"||op=="/"||op=="%"||op=="^"||op=="("||op==")";
}
inline bool isSpace(char c){
    return c==' '||c=='\t'||c=='\n'||c=='\r';
}
//格式化&分离表达式
list<string> toExpressionArray(string exp){
    string fexp;
    const char* data = exp.data();
    int idx = 0;
    int len = exp.length();
    for(;idx<len;idx++){
        char c = data[idx];
        if(isNumber(c)){
            fexp.push_back(c);
        }
        else if(!isSpace(c)){
            fexp.push_back(' ');
            fexp.push_back(c);
            fexp.push_back(' ');
        }
    }
    return Tokenize(fexp," ");
}

//中序换前序
list<string> m2l(list<string> m) {
	list<string> l;
	stack<string> s;
	string op;
	string y;
	s.push("#");
    for(list<string>::const_iterator i = m.begin();i!=m.end();i++){
	    op = *i;
	    if(op=="")
            continue;
	    if(!isSymbol(op)){
            l.push_back(op);
	    }else{
            if(icp[op]>isp[s.top()]){
                s.push(op);
            }else if(op==")"){
                y = s.top();
                s.pop();
                while(y!="("){
                    l.push_back(y);
                    y = s.top();
                    s.pop();
                }
            }else{
                y = s.top();
                s.pop();
                while(icp[op]<isp[y]){
                    l.push_back(y);
                    y = s.top();
                    s.pop();
                }
                s.push(y);
                s.push(op);
            }//if2
	    }//if1
	}//for
	while(s.top()!="#"){
	    l.push_back(s.top());
	    s.pop();
	}
	return l;
}
//计算
double _calc(double o1, double o2, char op) {
	switch(op){
	    case '+':{
            return o1+o2;
	    }
	    case '-':{
            return o1-o2;
	    }
	    case '*':{
            return o1*o2;
	    }
	    case '/':{
            return o1/o2;
	    }
	    case '^':{
            return pow(o1,o2);
	    }
	}
	return 0;
}
//计算前序表达式
double calc(list<string> in){
	stack<double> sk;
	for(list<string>::const_iterator i = in.begin();i!=in.end();i++){
	    string op = *i;
	    if(!isSymbol(op)){
            sk.push(atof(op.data()));
	    }else{
            double o2 = sk.top();
            sk.pop();
            double o1 = sk.top();
            sk.pop();
            char o = op.data()[0];
            double r = _calc(o1,o2,o);
            sk.push(r);
	    }
	}
	return sk.top();
}
//没用
void printList(list<string> l){
    int x=0;
    for(list<string>::const_iterator i = l.begin();i!=l.end();i++){
        cout<<++x<<":"<<*i<<endl;
    }
}
int main()
{
    isp["+"]=3;
	isp["-"]=3;
	isp["*"]=5;
	isp["/"]=5;
	isp["%"]=5;
	isp["^"]=5;
	isp["("]=1;
	isp[")"]=6;
	isp["#"]=0;

	icp["+"]=2;
	icp["-"]=2;
	icp["*"]=4;
	icp["/"]=4;
	icp["%"]=4;
	icp["^"]=4;
	icp["("]=6;
	icp[")"]=1;
	icp["#"]=0;

    string exp;
    cout<<"Exp:";
    cin>>exp;
    list<string> l1 = toExpressionArray(exp);
    printList(l1);
    list<string> l2 = m2l(l1);
    printList(l2);
    double r = calc(l2);
    cout<<"Result:"<<r<<endl;
    return 0;
}