Adding random generated numbers to arrays + averaging those arrays

Question

HW Question: We will simulate the throwing of dice. Again we will use Top-Down_Design to improve the readability, etc.

Generate 20 dice throws of two dies. Each die can generate a number of dots from 1 to 6. Add the two numbers together to get the value of the throw.

In one pass generate the 20 throws and store the numbers in an array.

In a second pass calculate the average of the numbers and display that on the console.

Seed the Random Number Generator with 8193 one time before getting any random numbers.

NOTE : We have not talked about passing a Array to functions. So for this assignment you can make the array of Dice throws global.

//I'm just confused to the concepts of adding the random generated numbers to arrays and then averaging them through the Top Down method.

 #include <iostream>
 #include <cstdlib>

using namespace std;

void Gen_20_Throws_Of_2_Die_And_Add_Values();
void Output_Avg(); //Calculates the average of the sum of the 20 rolls

int ArraySum[13]; // array for the numbers of 0-12 (13 total). Will ignore index array 0 and 1 later. array[13] = 12

int main()
{
    Gen_20_Throws_Of_2_Die_And_Add_Values();

    Output_Avg;

    cin.get();

    return 0;
}

void Gen_20_Throws_Of_2_Die_And_Add_Values()
{
    srand(8193); //seed random number generator with 8193

    int Dice_Throw_Number, Die1, Die2, Sum_Of_Two_Die;

    for (int Dice_Throw_Number = 1; Dice_Throw_Number <= 20; Dice_Throw_Number++)
    {
        Die1 = (rand() % 6 + 1);
        Die2 = (rand() % 6 + 1);

        Sum_Of_Two_Die = Die1 + Die2;

        ArraySum[Sum_Of_Two_Die] += 1;
    }
}

void Output_Avg()
{
    int Total_Of_20_Rolls, Average_Of_Rolls;

    for (int i = 2; i <= 12; i++) //ignores index of 0 and 1
    {
        Total_Of_20_Rolls += ArraySum[i];
    }

    Average_Of_Rolls = Total_Of_20_Rolls / 20;

    cout << "The average of 2 die rolled 20 times is " << Average_Of_Rolls;
}

Answer 1

Your code is a little confusing to follow, but I think I understand what's happening. Lets start with your Gen_20_Throws_Of_2_Die_And_Add_Values method.

int Dice_Throw_Number, Die1, Die2, Sum_Of_Two_Die;

for (int Dice_Throw_Number = 1; Dice_Throw_Number <= 20; Dice_Throw_Number++)
{
    Die1 = (rand() % 6 + 1);
    Die2 = (rand() % 6 + 1);

    Sum_Of_Two_Die = Die1 + Die2;

    ArraySum[Sum_Of_Two_Die] += 1;
}

You don't need to necessarily initialize int Dice_Throw_Number outside of the for loop. Feel free to make it inside the for loop. Also, I personally always find it easier to understand to start from zero and go up to only a < condition rather than a <=. So you'll have:

int Die1, Die2;

for (int Dice_Throw_Number = 0; Dice_Throw_Number < 20; Dice_Throw_Number++)
{
    Die1 = (rand() % 6 + 1);
    Die2 = (rand() % 6 + 1);

    //increment position of sum by 1
    ArraySum[Die1 + Die2] += 1;
}

Now in your Output_Average function, your logic is a lot off. You want to calculate what the average result was of throwing 2 die? Right now you're only adding how many times a certain total came up, not the total itself. So for example if you rolled 12 5 times, you'll adding 5 to the Total_Of_20_Rolls, not 60. That's easy to change, you just need to multiply.

int Total_Of_20_Rolls, Average_Of_Rolls;

for (int i = 2; i < 13; i++) //ignores index of 0 and 1
{
    Total_Of_20_Rolls += ArraySum[i] * i;
}

Average_Of_Rolls = Total_Of_20_Rolls / 20;

cout << "The average of 2 die rolled 20 times is " << Average_Of_Rolls;

That should help you out!