问错误：'*‘的操作数必须是指针，但具有"double“类型

EN

#include <iostream>

int main()
{
    double E;
    double R;
    double t;
    double C;
    
    std::cout << "This program will calculate the current flowing through an RC curcuit!\n\n";
    std::cout << "Please enter the power source voltage value in Volts: ";
    std::cin >> E;
    std::cout << "\n\n";
    std::cout << "Please enter the total resistance value in Ohms: ";
    std::cin >> R;
    std::cout << "\n\n";
    std::cout << "Please enter the time elapsed after the switch closed Seconds: ";
    std::cin >> t;
    std::cout << "\n\n";
    std::cout << "Please enter the total capacitance value in Farads: ";
    std::cin >> C;
    std::cout << "\n\n";
    double RC = R * C;
    double ER = E / R;
    double pow = -t / RC;
    double expo = 2.71828 ** pow; //this line is the problem...

    double I = ER * expo;
    std::cout << "The current flowing through this circuit is: " << I;

    return 0;
}