Function Practice

Function practice - dividing dice roll game into functions

Video Summary: https://youtu.be/jTx3XkffncU

Consider this solution to a previous exercise, which provided a looping game of rolling dice:

/*
Program name: diceroll.cpp
Author: Devon Blewett
Purpose: This program generates two random numbers between 1 and 6 and declares a winner between them, unless there is a draw

If the user enters y, it will loop.  If the user enters n, it will stop.  If the user enters something else, they will be prompted for correct input.

Written for the Open Textbooks program
*/
#include <iostream>
#include <time.h>
#include <string.h>
using namespace std;

int main(){
// Variable for user's choice to keep playing
// This could have been a char as well, but string will handle multiple letters when evaluating bad input
    string choice = "";
// Start the loop, and run until user enters 'n' or 'N'
// Checking the capital isn't required, but is good practice
    while(choice != "n" && choice != "N")
    {
// the values need to be assigned within the loop, or the rolls would never change
        srand(time(NULL));
        int dice1 = rand() % 6 + 1;
        int dice2 = rand() % 6 + 1;

cout << "Player one rolled " << dice1 << endl;
        cout << "Player two rolled " << dice2 << endl;
// player ones roll is higher
        if(dice1 > dice2){
            cout << "Player one wins!" << endl;
        }
// the players rolls are the same
        else if(dice1 == dice2){
            cout << "The players draw." << endl;
        }
// since there is only one more outcome, you do not need to check a condition here
        else{
            cout << "Player two wins!" << endl;
            }
        
        cout << "Would you like to roll again? Enter y for yes or n for no" << endl;
        cin >> choice;
// if the user entered bad input, prompt them again without the program advancing
        while(choice != "y" && choice != "Y" 
            && choice != "n" && choice != "N")
        {
            cout << "You must enter y for yes or n for no" << endl;
            cin >> choice;
        } 
    }
// When the user enters n, they will end up here
    cout << "The game has ended" << endl;
	return 0;
}

The goal of this exercise is to divide the functionality up into the following functions without breaking the game:

int rollDice() - Generates and returns a single random number
void checkResult(int dice1, int dice2) - Takes two int input, evaluates which is larger, and prints the winner (or draw)
void userPrompt(string& choice) - Takes the reference of a string choice. Prompts the user to play again. If the user presses y, the value of choice is changed to 'y', if the user presses n, the value is changed to 'n', and if the input is not valid the user is prompted again

In general, this exercise can mostly be completed by copy and pasting the existing code into the appropriate functions, and then adding appropriate function calls to the main program. The output should remain the same as what you start with.

Solution

/*
Program name: diceroll.cpp
Author: Devon Blewett
Purpose: This program generates two random numbers between 1 and 6 and declares a winner between them, unless there is a draw

If the user enters y, it will loop.  If the user enters n, it will stop.  If the user enters something else, they will be prompted for correct input.

The program has been divided up into functions for rolling the dice, checking the result, and prompting the user.

Written for the Open Textbooks program
*/
#include <iostream>
#include <time.h>
#include <string.h>
using namespace std;

// Function prototypes go here
// function returns int from when dice is rolled
int rollDice();
// since function just prints out the winner, does not return a value
void checkResult(int dice1, int dice2);
// since this changes the variable, it does not return a string
void userPrompt(string& choice);

cout << "Player one rolled " << dice1 << endl;
        cout << "Player two rolled " << dice2 << endl;
        
// need to pass the dice rolls in order to check them
        checkResult(dice1, dice2);

// need to pass choice, but since it is by reference the value in choice is changed, and there is no need for a return
        userPrompt(choice);

}
// When the user enters n, they will end up here
    cout << "The game has ended" << endl;
	return 0;
}

// function definitions go here

/*
function name: rollDice
parameters: none
purpose: generates a random value between 1 and 6
*/
int rollDice(){
    return rand() % 6 + 1;
}

/*
function name: checkResult
parameters: two ints representing the dice values
purpose: Checks which dice value is higher, and prints an appropriate message
*/
void checkResult(int dice1, int dice2){
    // player ones roll is higher
        if(dice1 > dice2){
            cout << "Player one wins!" << endl;
        }
// the players rolls are the same
        else if(dice1 == dice2){
            cout << "The players draw." << endl;
        }
// since there is only one more outcome, you do not need to check a condition here
        else{
            cout << "Player two wins!" << endl;
        }
}

/*
function name: userPrompt
parameters: string choice, passed by reference
purpose: Check if the user wants to keep playing.  Keeps prompting until it receives y or n
side effects: string choice value is changed in main
*/
void userPrompt(string& choice){
            cout << "Would you like to roll again? Enter y for yes or n for no" << endl;
        cin >> choice;
// if the user entered bad input, prompt them again without the program advancing
        while(choice != "y" && choice != "Y" 
            && choice != "n" && choice != "N")
        {
            cout << "You must enter y for yes or n for no" << endl;
            cin >> choice;
        } 
}

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