您没有创建任何函数，只是向main添加了几行代码。创建函数和数据结构对于保持代码的可读性和可维护性非常重要。
对于SO来说，代码编译和任何文件I/O模拟也很重要，这样我们就可以在我们最喜欢的（在线）编译器中测试代码。如本例所示：https://onlinegdb.com/_KJLAq6mK

#include <iostream>
#include <fstream>
#include <numeric> // for accumulate
#include <sstream>
#include <vector>  // for vector a dynamically resizable array

// using namespace std; <== no don't use this.

// simulate an input file
// by providing a load function that accepts an std::istream&
// you can use both a real input file or any other input stream
// to load from.
std::istringstream simulated_file
{
    "4\n"
    "100.0\n"
    "2000.0\n"
    "3500.0\n"
    "10000.0\n"
};

// when you have data that is related 
// like it needs to be read from file
// declare a class or struct;
struct Circuit
{
    // make small functions
    double average_resistance()
    {
        if (resistances.empty()) return 0.0;
        auto total_resistance = std::accumulate(resistances.begin(), resistances.end(), 0.0);
        return total_resistance / static_cast<double>(resistances.size());
    }

    // when you have more then 1 thing it is an array or vector
    //double resistor1, resistor2, resistor3, resistor4, resistor5, resistor6;
    std::vector<double> resistances;
};

Circuit load(std::istream& is)
{
    Circuit circuit{};
    std::size_t number_of_resistors;
    double resistance;

    is >> number_of_resistors;
    for (std::size_t n{0ul}; n < number_of_resistors; ++n)
    {
        is >> resistance;
        circuit.resistances.push_back(resistance);
    }

    return circuit;
}

int main() 
{
    //int resistors_in_parallel; should have been a double
    // by making functions your code becomes a lot more readable
    auto circuit = load(simulated_file);

    std::cout << std::format("The resistance is {} ohms when connected in parallel.", circuit.average_resistance());

    return 0;
}