00_review_02_histogram

Review 02 - Arrays - Histogram

• Accept 00_review_02_histogram
• Get main.cpp
• Get histogram.h

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Description

Write a program to plot out a simple version of the "bell curve" or "normal distribution" based on the sum of 4 random dice rolls.

What you will learn

After completing this program you should be able to:

• Prototype and write the implementation of a function
• Understand array indexing
• Understand how to use loops to iterate over arrays
• Introduce randomness into your program

Background Information and Notes

The "normal distribution" is a very important family of probability distributions. If you take any random event that produces numerical values, and repeat it often, the average of those values, although random, behaves in a predictable way. In this lab we are using only a small number of rolls (4), which is not infinite, but enough to yield a curve that resembles the bell curve.

Here is a sample run of your program: How many rolls do you want? 500 (this is the user input)

 4: 
 5:X 
 6:XXX 
 7:XXXXXXXXXXXXXX 
 8:XXXXXXXXXXXXXX 
 9:XXXXXXXXXXXXXXXXXXXXXXX 
10:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
11:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
12:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
13:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
14:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
15:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
16:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
17:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
18:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
19:XXXXXXXXXXXXXXXXXX 
20:XXXXXXXXXX 
21:XXX 
22:XX 
23: 
24:X

In this example, we asked the program to simulate 500 4-dice rolls. The sum was never four, the sum was five on 1 of the 500 trials, the sum was six on 3 of the trials, etc.

Functions

Implement functions in includes/histogram/histogram.h

int roll()

Define a function roll() that takes no arguments, and returns a random integer from 1 to 6. Before proceeding further, we recommend you write a short main method to test it out and make sure it gives you the right values.

int generateHistogramArray()

Implement the following function to update the histogram counts array:

void generateHistogramArray (int counts[], int rolls);

int counts[] is the int array to save the sum of points of four dices int rolls is the numbers of rolling dices, for example 500

void printHistogram(int counts[])

Before moving on to the logic to add up rolls and count them, we will implement a function that encapsulates the output display of our sums. You will write a function void printHistogram(int counts[]) that takes an array of integers (assumed to be of size 21 elements), then prints out sequential labeled lines from 4 to 24 with as many X symbols on that line as is indicated in the appropriate element of the array (i.e. counts[i]). We start our labels at 4 since rolling 4 dice can't produce a sum of 0- 3 (i.e. index 0 of the array corresponds to roll totaling 4, index 1 to a roll totaling 5, index 2 a roll totaling 6, …, and index 20 to a roll totaling 24).

Let's test our printHistogram function by writing a sample main() that calls it. We will fill in a dummy array and just ask printHistogram to print it out. You should try the same and ensure your printHistogram is working with our dummy main():

int main()
{
  int testCounts[21]; // 21 options of sum of 4 dice => [4,24]
  for (int i=0; i<21; i++)
    testCounts[i] = i; // fill the array printHistogram(testCounts); //fill your method
}

it should produce the following output:

 4:X
 5:XX
 6:XXX
 7:XXXX
 8:XXXXX
 9:XXXXXX
10:XXXXXXX
...
24:XXXXXXXXXXXXXXXXXXXXX

int main()

Finally, write the main function of the program. (Comment out all the other test main methods you used earlier.) It should

• Ask the user for a number, call it n
• Run n experiments, where each experiment rolls 4 dice and adds them up
• Throughout the experiments, keeps track of how often each possible sum (from 4 to 24) occurred
• Prints out the histogram showing how many times each sum occurred (so in total it should print out n of the X symbols)
• Your program should give different results each time it runs. Make sure you seed the random number generator appropriately.