理解

struct Re2_str_dou{
	string Str="";
	double Dou=0;
};
struct Re2_int_int{
	int Start=0;
	int End=0;
};
Re2_int_int Bracket_found(string Sentence)
{
	Re2_int_int Ret;
	int num=-1,a=0,b=0,total=0;//,copy=Sentence.size();
	Ret.Start=Sentence.find('(');
	Sentence.erase(Ret.Start,1);
	while(!num){
		//cout<<num<<endl;
		a=Sentence.find('(');
		b=Sentence.find(')');
		if(a!=-1){//cout<<'a';
			if(!num)break;
			num--;
			Sentence.erase(a,1);
			total++;
		}
		if(b!=-1){//cout<<'b';
			if(!num)break;
			num++;
			Sentence.erase(b,1);
			total++;
		}
	}
	Ret.End=b+total;
	//cout<<"b="<<b<<endl;
	return Ret;
}
Re2_str_dou Mon(string Monomial)
{	Re2_str_dou Re;
	//cout<<Monomial<<endl;
	short Id=0;
	if(Monomial[0]=='-')Id=-1;
	else Id=1;
	//cout<<Id;
	if(Monomial[0]=='-' || Monomial[0]=='+')Monomial.erase(0,1);
	while(
		Monomial[0]>='0' && Monomial[0]<='9' || 
		Monomial[0]=='.' || Monomial[0]=='x' || 
		Monomial[0]=='*' || Monomial[0]=='p'){
		//cout<<Monomial<<endl;
		if(Monomial[0]>='0' && Monomial[0]<='9' || Monomial[0]=='.')
		{
			short Flag=0;
			double Add=0;
			while(Monomial[0]>='0' && Monomial[0]<='9' || Monomial[0]=='.')
			{
				if(Flag){
					Add+=(double)(Monomial[0]-'0')/Flag;
					Flag*=10;
				}else{
					Add*=10;
					Add+=(double)(Monomial[0]-'0');
				}
				Monomial.erase(0,1);
				if(Monomial[0]=='.'){
					Flag=10;
					Monomial.erase(0,1);
				}
			}
			if(Re.Dou || Re.Dou)Re.Dou*=Add;
			else if(!Re.Dou)Re.Dou=Add;
		}
		if(Monomial[0]=='*')Monomial.erase(0,1);
		if(Monomial[0]=='x'){
			if(Re.Dou && x)Re.Dou*=x;
			else Re.Dou=x;
			Monomial.erase(0,1);
		}
		if(Monomial[0]=='p' && Monomial[1]=='o' && Monomial[2]=='w' && Monomial[3]=='('){
			//cout<<'a';
			Monomial.erase(0,4);
			double Base=0,Index=0,ad=0;
			Re2_str_dou Re1;
			Re1=Mon(Monomial);
			Base=Re1.Dou;
			Monomial=Re1.Str;
			Monomial.erase(0,1);//cout<<Monomial;
			Re1=Mon(Monomial);
			Index=Re1.Dou;
			Monomial=Re1.Str;
			Monomial.erase(0,1);
			//cout<<"B"<<Base<<"I"<<Index<<' ';
			ad=pow(Base,Index);
			if(Re.Dou && ad)Re.Dou*=ad;
			else Re.Dou=ad;
		}
	}
	Re.Str=Monomial;
	Re.Dou*=Id;
	//cout<<Re.Dou<<endl;
	return Re;
}
double STR(string Monomial)
{
	Monomial.erase(0,2);
	string Mo="";
	double Sum=0;
	short Id=1;
	Re2_str_dou S;
	while(Monomial!="")
	{
		//cout<<'a';
		Mo="";
		Id=1;
		if(Monomial[0]=='-')Id=-1;
		if(Monomial[0]=='+' || Monomial[0]=='-')Monomial.erase(0,1);
		//cout<<Monomial<<endl;
		while(
		Monomial[0]>='0' && Monomial[0]<='9' || 
		Monomial[0]=='.' || Monomial[0]=='x' || 
		Monomial[0]=='x' || Monomial[0]=='p' ||
		Monomial[0]=='o' || Monomial[0]=='w' ||
		Monomial[0]=='(' || Monomial[0]==')' ||
		Monomial[0]==',' || Monomial[0]=='*'   )
		{
			if(Monomial[0]=='p'){//cout<<'b';
				Re2_int_int S1=Bracket_found(Monomial);
				//cout<<"VCR"<<S1.Start<<' '<<S1.End<<endl;
				for(int i=0;i<=S1.End;i++){
					Mo+=Monomial[0];
					Monomial.erase(0,1);
				}
			}else{
				Mo+=Monomial[0];
				Monomial.erase(0,1);
			}
		}
		if(Id==-1)Mo='-'+Mo;
		S=Mon(Mo);
		//cout<<S.Dou<<endl;
		Sum+=S.Dou;
		//cout<<Monomial<<' '<<Mo<<' '<<S.Dou<<endl;
	}
	return Sum;
}