Multiply complex object with real and imaginary parts by a multiplier of type 'double' in C++

I am trying to multiple every element of a complex array by a multiplying factor, for the application of fourier transform. I am applying a hanning window filter to a complex file of a wave function.

I am working in C++ with CodeBlocks, I keep getting -->

error: invalid types 'double[int]' for array subscript

My code is here:

#include <iostream>
#include <fstream>
#include <string>
#include <regex>
#include <cmath>
#define PI 3.14159265359
using namespace std;

class Complex {
    public:
        Complex();
        Complex(double realNum);
        Complex(double realNum, double imagNum);

        //Complex(double real = 0.0, double imaginary = 0.0); This avoids the 3 above?
        Complex(const Complex& obj);
    private:
       double real;
       double imaginary;
 };

Complex::Complex(const Complex& obj) {
    real = obj.real;
    imaginary = obj.imaginary;
}

Complex::Complex () {
   real = 0;
   imaginary = 0;
}

Complex::Complex (double realNum) {
    real = realNum;
    imaginary = 0;
}

Complex::Complex (double realNum, double imagNum) {
   real = realNum;
   imaginary = imagNum;
}

int main () {
    Complex *complexArray = new Complex[1000];
    ifstream myfile("myfile.txt");
    /* this will match the complex numbers of the form - 123.123 + 14.1244  or 123 - 1343.193 and so on,
      basically assumes that both the real and the imaginary parts are both doubles*/
    regex reg_obj("^[ ]*([-]?\\d+(\\.\\d+)?)\\s*([+-])\\s*(\\d+(\\.\\d+)?)i");
    smatch sm;
    string line;
    int i = 0;
    double real, imag;
    if (myfile.is_open()) {
        while (! myfile.eof()) {

            getline(myfile, line);
            if(regex_search(line, sm, reg_obj)){
                real = stod(sm[1]);       // this ([-]?\\d+(\\.\\d+)?) is group 1 and will match the real part of the number
                imag = stod(sm[4]);       // second group (\\d+(\\.\\d+)?)i is group 4 which matches the imaginary part of the complex number without matching + or - which are taken care of separately because there could be space between the +|- symbol and the imaginary part
                if(sm[3]=="-") imag = -imag;
                complexArray[i] = Complex(real, imag);
                i++;
            }
            // Hanning Window
            for (int i = 0; i < 1000; i++) {
                double multiplier = 0.5 * (1 - cos(2*PI*i/999));
                complexArray[i] = multiplier[i] * complexArray[i];
                }
        }

        myfile.close();
     }else {
        cout << "Error. Could not find/open file." ;
     }
     cout << complexArray << endl;
     return 0;
};

I would like to multiply each element of the complex object by each element in the multiplication array. I'm not sure of the correct way to do this.

For starters in this loop

        for (int i = 0; i < 1000; i++) {
            double multiplier = 0.5 * (1 - cos(2*PI*i/999));
            complexArray[i] = multiplier[i] * complexArray[i];
            }

the variable multiplier is declared as a scalar object of the type double. So you need to write

complexArray[i] = multiplier * complexArray[i];

instead of

complexArray[i] = multiplier[i] * complexArray[i];

Also you need to overload the operator * for your class.

For example

class Complex {
    public:
        Complex();
        Complex(double realNum);
        Complex(double realNum, double imagNum);

        //Complex(double real = 0.0, double imaginary = 0.0); This avoids the 3 above?
        Complex(const Complex& obj);

        friend const Complex operator *( double, const Complex & );
    private:
       double real;
       double imaginary;
};

//...

const Complex operator *( double value, const Complex &c )
{
    return { value * c.real, value * c.imaginary };
}

Also the condition in the while loop

    while (! myfile.eof()) {

        getline(myfile, line);
        //...

substitute for

    while ( getline(myfile, line) ) {
        //...

And this loop

        for (int i = 0; i < 1000; i++) {
            double multiplier = 0.5 * (1 - cos(2*PI*i/999));
            complexArray[i] = multiplier[i] * complexArray[i];
            }

should be outside the while loop. For example

        for ( int j = 0; j < i; j++) {
            double multiplier = 0.5 * (1 - cos(2*PI*i/999));
            complexArray[j] = multiplier * complexArray[j];
            }