Nested While Loop Runs Once More Than Expected - c++

Question

I am new to C++ (have been using it for around 2 weeks), and right now I am trying to write a program that will roll a dice and give a random number between 1 and 6, then count how many rolls it takes to get a 6. After that, it will ask user if they want to continue with a positive and exit with 0.
If the input here is 0, then show the average rolls to get a 6 and the number of 6 occurrences that the average was based on, and all of this using do-while and/or while loops.
The problem is, whenever I press 0, the program seems to run the inner loop one more time before exiting and showing the averages.
#include <iostream>
#include <ctime>
#include <cstdlib>
using namespace std;
int main()
{
float number_rolls, number_sixes;
int x;
number_rolls = 0; // store the number of rolls made
number_sixes = 0; // store the number of sixes
x = 0;
srand(time(0));//initialise random num generator using time
int roll = 0;//declare a variable to keep store the random number
do
{
cout << "possitive to continue, 0 to exit" << endl;
cin >> x;
do
{
roll = rand() % 6 + 1; //generate a random number between 1 and 6
number_rolls = number_rolls++; // add the rolls to a counter
cout << roll << endl; // out put the roll values
} while (roll != 6);
number_sixes = number_sixes++; // adds the sixes to a counter
} while (x != 0);
cout << "average rolls to get a six: " << number_rolls / number_sixes << " you took; " << number_rolls << "rolls and got: " << number_sixes << " sixes" << endl;
Can somebody please help point me in the right direction?

Answer 1

After reading the value of x, you can compare it to 0 and break out of the loop immediately:
do {
cout << "possitive to continue, 0 to exit" << endl;
cin >> x;
// Add this check
if (x == 0)
break; // if this is reached, the inner `do-while` is not executed
do {
// ...
} while (roll != 6);
number_sixes = number_sixes++; // adds the sixes to a counter
} while (x != 0);
Now this makes the check in the outer while is unnecessary, and you can convert the do-while to a while loop with a true condition:
while (true) {
cout << "possitive to continue, 0 to exit" << endl;
cin >> x;
if (x == 0)
break; // if this is reached, the inner `do-while` is not executed
do {
// ...
} while (roll != 6);
number_sixes = number_sixes++; // adds the sixes to a counter
}