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Running mean and variance

brachburton1 (11)
Almost done with my dice roll simulator which simulates a roll given a XdY user input.

There's only two problems: that my mean and standard deviation are all out of wack on option 2 (which performs a dice roll multiple times), and that my cin.fail() in option 2 is catching integers as well instead of just input with chars.

I'm sure that the first one is because I have the formula for mean and standard deviation written wrong, but I just couldn't seem to understand how to write it when I googled it.

Honestly no idea why the cin.fail() would catch on the other problem.

I appreciate the help 

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#include <iostream>
#include <ctime>
#include <sstream>
#include <string>
#include <iomanip>
#include <cmath>

using namespace std;

const int OPTION_SINGLE_ROLL = 1;
const int OPTION_MULTI_ROLL = 2;
const int OPTION_QUIT = 3;


int simulate_dice_roll (int x, int y) {    // simulates dice roll based on XdY input
    int result = 0;
    for (int i = 0; i < x; i++) {
        result += rand() % y + 1;
    }
    return result;
}

int extract_x (string dice_info_xdy) {   // extracts X value from XdY string input
    stringstream ss;
    ss << dice_info_xdy.substr(0, dice_info_xdy.find("d"));
    int x;
    ss >> x;
    return x;
}

int extract_y (string dice_info_xdy) {    // extracts Y value from XdY string input
    stringstream ss;
    ss << dice_info_xdy.substr(dice_info_xdy.find("d") + 1);
    int y;
    ss >> y;
    return y;
}

int validity_check (int x, int y, string dice_info_xdy){
    int invalid;
    if (x < 1 || y < 1 || dice_info_xdy.find("d") == -1) { // resets option if input is
        cout << "Invalid input." << endl;                  // invalid
        invalid = 1;
    }
    return invalid;
}

int main() {
    srand(time(NULL));
    bool return_to_root_menu;
    bool return_to_option_1;
    bool return_to_option_2;
    bool return_to_num_rolls;
    do {
        cout << "\t\t\t***ROOT MENU***\nPlease select one of the following options:\n1 - Simulate a single dice roll\n2 - Simulate multiple dice rolls\n3 - Quit the program\n";
        int option_choice;
        cin >> option_choice;
        cin.fail(); { // resets to root menu if a character or string is input instead of an int
            cin.clear();
            cin.ignore(1000, '\n');
        }
        if (option_choice == OPTION_SINGLE_ROLL){
            do {
                cout << "Please specify roll in XdY format: ";
                string dice_info_xdy;
                cin >> dice_info_xdy;
                int x, y;
                x = extract_x(dice_info_xdy);
                y = extract_y(dice_info_xdy);
                if (validity_check(x, y, dice_info_xdy) == 1) {
                    continue;
                }
                int result = simulate_dice_roll(x, y);
                cout << "Result: " << result << endl; // displays result of dice roll
                return_to_option_1 = true;
            } while (return_to_option_1 == false);
        }
        if (option_choice == OPTION_MULTI_ROLL) {
            do {
                cout << "Please specify roll in XdY format: ";
                string dice_info_xdy;
                cin >> dice_info_xdy;
                int x, y;
                x = extract_x(dice_info_xdy);
                y = extract_y(dice_info_xdy);
                if (validity_check(x, y, dice_info_xdy) == 1) {
                    continue;
                }
                do {
                    cout << "Please enter amount of times you would like to execute this roll: ";
                    int num_rolls;
                    cin >> num_rolls;
                    cin.fail(); { // resets to num rolls prompt if char is input
                        cin.clear();
                        cin.ignore(1000, '\n');
                        continue;
                    }
                    if (num_rolls < 1){ // resets to num rolls prompt if number less than 0 is input
                        continue;
                    }
                    if (num_rolls >= 1){
                        double total_result = 0;
                        double new_mean = 0;
                        double mean = 0;
                        double variance = 0;
                        for (int i = 0; i < num_rolls; i++){ // supposed to find running mean and standard
                            total_result = simulate_dice_roll(x, y);  //variation
                            mean = total_result / (i + 1);
                            new_mean += ((i + 1) - mean) / i;
                            variance += ((i + 1) - new_mean) * ((i + 1) - mean);
                        }
                        double std_deviation = sqrt(variance / (num_rolls - 1));
                        cout << "Min: " << x << "\nMax: " << x * y << "\nMean: " << new_mean << "\nStdDev: " << std_deviation << endl;
                    }
                    return_to_num_rolls = true; // ends num rolls loop
                } while (return_to_num_rolls == false);
                return_to_option_2 = true; // ends option 2 loop
            } while (return_to_option_2 == false);
            
        }
        if (option_choice == OPTION_QUIT) {
            cout << "Goodbye!";
            return_to_root_menu = true;
            continue;
        }
        return_to_root_menu = false; // resets to root menu when program is finished
        continue;
        return 0;
    } while (return_to_root_menu == false);
}
Last edited on
TheKingOfTyrants (232)
A couple things I notice right off the bat is that code below will always execute. I believe you want to clear/ignore/continue when cin.fail() returns true, but that means you have to wrap everything into an if statement.

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//lines 58-61
//runs cin.fail() and cin.clear() and cin.ignore() run regardless of what cin.fail() returns
cin.fail(); { // resets to root menu if a character or string is input instead of an int
            cin.clear();
            cin.ignore(1000, '\n');
        }

//lines 93-96
//runs cin.fail() and cin.clear(), cin.ignore(), continue run regardless of what cin.fail() returns
cin.fail(); { // resets to num rolls prompt if char is input
                        cin.clear();
                        cin.ignore(1000, '\n');
                        continue;
                    }
brachburton1 (11)
Awesome, thank you. Totally obvious now that I think about it.

I also seemed to have fixed the mean and stdDev.

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#include <iostream>
#include <ctime>
#include <sstream>
#include <string>
#include <iomanip>
#include <cmath>

using namespace std;

const int OPTION_SINGLE_ROLL = 1;
const int OPTION_MULTI_ROLL = 2;
const int OPTION_QUIT = 3;


int simulate_dice_roll (int x, int y) {    // simulates dice roll based on XdY input
    int result = 0;
    for (int i = 0; i < x; i++) {
        result += rand() % y + 1;
    }
    return result;
}

int extract_x (string dice_info_xdy) {   // extracts X value from XdY string input
    stringstream ss;
    ss << dice_info_xdy.substr(0, dice_info_xdy.find("d"));
    int x;
    ss >> x;
    return x;
}

int extract_y (string dice_info_xdy) {    // extracts Y value from XdY string input
    stringstream ss;
    ss << dice_info_xdy.substr(dice_info_xdy.find("d") + 1);
    int y;
    ss >> y;
    return y;
}

int validity_check (int x, int y, string dice_info_xdy){
    int invalid;
    if (x < 1 || y < 1 || dice_info_xdy.find("d") == -1) { // resets option if input is
        cout << "Invalid input." << endl;                  // invalid
        invalid = 1;
    }
    return invalid;
}

int main() {
    srand(time(NULL));
    bool return_to_root_menu;
    bool return_to_option_1;
    bool return_to_option_2;
    bool return_to_num_rolls;
    do {
        cout << "\t\t\t***ROOT MENU***\nPlease select one of the following options:\n1 - Simulate a single dice roll\n2 - Simulate multiple dice rolls\n3 - Quit the program\n";
        int option_choice;
        cin >> option_choice;
        if (cin.fail() == true) { // resets to root menu if a character or string is input instead of an int
            cin.clear();
            cin.ignore(1000, '\n');
        }
        if (option_choice == OPTION_SINGLE_ROLL){
            do {
                cout << "Please specify roll in XdY format: ";
                string dice_info_xdy;
                cin >> dice_info_xdy;
                int x, y;
                x = extract_x(dice_info_xdy);
                y = extract_y(dice_info_xdy);
                if (validity_check(x, y, dice_info_xdy) == 1) {
                    continue;
                }
                int result = simulate_dice_roll(x, y);
                cout << "Result: " << result << endl; // displays result of dice roll
                return_to_option_1 = true;
            } while (return_to_option_1 == false);
        }
        if (option_choice == OPTION_MULTI_ROLL) {
            do {
                cout << "Please specify roll in XdY format: ";
                string dice_info_xdy;
                cin >> dice_info_xdy;
                int x, y;
                x = extract_x(dice_info_xdy);
                y = extract_y(dice_info_xdy);
                if (validity_check(x, y, dice_info_xdy) == 1) {
                    continue;
                }
                do {
                    cout << "Please enter amount of times you would like to execute this roll: ";
                    int num_rolls;
                    cin >> num_rolls;
                    if (cin.fail() == true) { // resets to num rolls prompt if char is input
                        cin.clear();
                        cin.ignore(1000, '\n');
                        continue;
                    }
                    if (num_rolls < 1){ // resets to num rolls prompt if number less than 0 is input
                        continue;
                    }
                    if (num_rolls >= 1){
                        double total_result = 0;
                        double mean = 0;
                        double variance = 0;
                        double std_deviation = 0;
                        double total_result1 = 0;
                        double array[num_rolls];
                        for (int i = 0; i < num_rolls; i++){ // supposed to find running mean and standard
                            array[i] = simulate_dice_roll(x, y);
                            total_result += array[i];
                        }
                        mean = total_result / num_rolls;
                        for (int i = 0; i < num_rolls; i++){ // supposed to find running mean and standard
                            total_result1 += pow((array[i] - mean), 2);
                        }
                        variance = total_result1 / num_rolls;
                        std_deviation = sqrt(variance);
                        cout << "Min: " << x << "\nMax: " << x * y << "\nMean: " << mean << "\nStdDev: " << std_deviation << endl;
                    }
                    return_to_num_rolls = true; // ends num rolls loop
                } while (return_to_num_rolls == false);
                return_to_option_2 = true; // ends option 2 loop
            } while (return_to_option_2 == false);
            
        }
        if (option_choice == OPTION_QUIT) {
            cout << "Goodbye!";
            return_to_root_menu = true;
            continue;
        }
        return_to_root_menu = false; // resets to root menu when program is finished
        continue;
        return 0;
    } while (return_to_root_menu == false);
}
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