为什么我的函数不返回字符串？

Question

I created a function (displayChoice) to generate a random number and then created another function (getComputerChoice) to take that number and assign that random integer to a string. When I print that string, nothing appears. I am lost as to why this happens.

#include <iostream>
#include <limits>
#include <ctime>
#include <cstdlib>
int getComputerChoice();
std::string displayChoice(int dChoice);


int main()
{

std::string comp = displayChoice(getComputerChoice());
std::cout << comp;
}
int getComputerChoice()
{
  srand(time(NULL));
  int ranCompChoice = (rand() % 6) + 1;
  return ranCompChoice;
}


std::string displayChoice(int dChoice)
{
std::string ChoiceString;
if (dChoice == 1)
{
    ChoiceString == "rock";

}
else if (dChoice == 2)
{
    ChoiceString == "paper";
}
else if (dChoice == 3)
{
    ChoiceString == "scissors";
}
else if (dChoice == 4)
{
    ChoiceString == "lizard";
}
else
{
    ChoiceString == "Spock";
}
    return ChoiceString;
}

Answer 1

You have to use the assignment operator.

eg ChoiceString = "Spock";