转换为double后的字符串拆分和乘法

我试图写一个函数，它得到字符串作为它的参数，搜索如果有'p'或'e'在它，分割到单独的字符串，取代"p"与"3.14…"answers"e" with "2.71…"，将所有字符串转换为double，然后将所有转换后的字符串相乘。例如，当参数为"123.45p4e9.2"时，函数将其拆分为"123.45"， "p"， "4"， "e"answers"9.2"，然后用常量替换字符:"123.45"， "3.14…， "4"， "2.71…"answers"9.2"，然后将它们全部转换为双精度并相乘:123.45*3.14*4*2.71*9.2。

问题是，当我给它一个字符串只有一个数字，没有任何'p'或'e'(例如"2.4"或"32")，它返回0。然而,当我给它"e "、" p ",或" ep ",它返回" 2.71……"、" 3.14……8.53…"，所以在这种情况下它工作得很好。问题又回来了，当我试图给它字符串与数字和字符的组合。当我输入"3p"，函数返回正确的结果:"9.42…"。另一方面，当我输入"p3"时，它返回"3.14…"，尽管它仍然应该是"9.42…"。看起来它根本无法处理数字，如果出现'e'或'p'，它似乎无法发现第一个字符之后的数字。

有人能看看代码并找出问题在哪里吗?我已经找了好几个小时了，但从逻辑上讲，一切似乎都没问题。

#include "stdafx.h"
#include <iostream>
#include <conio.h>
#include <string>
#include <math.h>
#include <windows.h>
#define NULL       "null"
using namespace std;
double stale(string w);
int main(){
//Testing the function
string liczba;
cout << "Type the number: ";
cin >> liczba;
double wynik = stale(liczba);
cout << endl << "Result: " << wynik << endl << endl;
system("PAUSE");

}
double stale(string w){
string *wartosc = new string[w.length()];     //Dynamic string array
for(int i = 0; i < w.length(); i++){          //String array is filled with "null"
    wartosc[i] = NULL;
}
{          //Bracket only to control lifespawn of liczba and element_wartosc variables
string liczba = NULL;           // There'll be built a number between e and p
int element_wartosc = 0;
for(int i = 0; i < w.length(); i++){          //Searching argument string for e and p
    switch(w[i]){
    case 'p':
        if(liczba != NULL){                   //Ends generating number, which isn't e or p
            wartosc[element_wartosc] = liczba;
            liczba = NULL;
            element_wartosc++;
            wartosc[element_wartosc] = "3.14159265358979323846";
            element_wartosc++;
        }else{
        wartosc[element_wartosc] = "3.14159265358979323846";
        element_wartosc++;
        }
        break;
    case 'e':
        if(liczba != NULL){                   //Ends generating number, which isn't e or p
            wartosc[element_wartosc] = liczba;
            liczba = NULL;
            element_wartosc++;
            wartosc[element_wartosc] = "2.71828182845904523536";
            element_wartosc++;
        }else{
        wartosc[element_wartosc] = "2.71828182845904523536";
        element_wartosc++;
        }
        break;
    default:
        if (liczba == NULL){
            liczba = w[i];                        //Starts filling liczba variable with first character
        }else if(w[i] == ''){ 
            wartosc[element_wartosc] = liczba;    //Ends generating number on argument string end
            break;
        }else{
            liczba = liczba + w[i];               //Builds the number
        }
    }
}
}
double wynik = 0;                              //There will be the result
for(int i = 0; i < w.length(); i++){
    if(wartosc[i] == NULL){                    //wartosc array was filled earlier with "null" strings, to distinguish it from entered numbers
        continue;
    }else{
        double liczba = stod(wartosc[i]);      //Converting strings onto doubles
        if(wynik == 0){
            wynik = liczba;                    //Starting multiplification
        }else{
            wynik *= liczba;                   //Multiplification
        }
    }
}
delete[] wartosc;      //Removing dynamic array
return wynik;          //The result is returned
}