Nova's Basic C++ Calculator

// Nova's C++ Calculator v1.1
/*
Updates and other information

[NEW]**
- Tried using switches for math, might just do separate "if functions" if problem persists.

[BUGS]**
- Only multiplication works at the moment.
- Line 45
*/
#include <iostream>
#include <string>

int main()
{
    double digit1;
    double digit2;
    int process;
    double answer;
    //information gathering process
  std::cout << "Simple Calculator by Nova\n";
  std::cout << "Please enter your first number: ";
  std::cin >> digit1; //grabbing digit1 from user
  std::cout << "\n";
  std::cout << "Please enter your second number: ";
  std::cin >> digit2; //grabbing second digit
  std::cout << "\n";
  //menu
  std::cout << "--------------------------------\n";
  std::cout << "1 - Multiply\n";
    std::cout << "2 - Divide\n";
      std::cout << "3 - Add\n";
        std::cout << "4 - Subtract\n";
          std::cout << "--------------------------------";
  std::cout << "\n";
  std::cout << "Please select a process using a single digit: ";
  std::cin >> process;
  std::cout << "\n";
  if (process >= 5 || process < 1)
    {
        //Invalid Value Error [BUG 1 - LINE 45]
        std::cout << "[Error: Invalid Selection]\n";
        std::cout << "\n";
        std::cout << "Please select a process using a single digit: ";
        std::cout << "[WARNING] If you select a number that isn't on the list, the program will exit. (Currently working on a fix.";
        std::cin >> process;
    }

    if (process = 1) {

            answer = (digit1 * digit2);
                std::cout << "Answer: " << answer << "\n";
    std::cout << "Run the program again to restart the process.";

			digit1++;
			digit2++;

        } switch (process = 2) {

            answer = (digit1 / digit2);
                std::cout << "Answer: " << answer << "\n";
    std::cout << "Run the program again to restart the process.";

			digit1++;
			digit2++;

        } switch (process = 3) {
        if (process = 3){

            answer = (digit1 + digit2);
                std::cout << "Answer: " << answer << "\n";
    std::cout << "Run the program again to restart the process.";

			digit1++;
			digit2++;
        } switch (process = 4) {

            answer = (digit1 - digit2);
                std::cout << "Answer: " << answer << "\n";
    std::cout << "Run the program again to restart the process.";

			digit1++;
			digit2++;

        }


    }

}