CSCI 261/Lab07C

LAB 07C - MEET THE ARRAY

Concepts

The goal of this assignment is to gain practice with arrays: how to declare (and initialize) arrays, how to access array values, and how to store values in arrays.

Collections of Things

To date, you've focused mostly on working with data one "piece" at a time. But in the real world, we're often concerned with collections of data: scores, hourly air temperatures, pressure readings over time, and colors of socks. In computer science, we call these collections "data structures" -- things that contain data. Perhaps the most simple data structure is the array: a container that holds multiple instances of only one type of thing. For example, you might have an array called scores that contains a bunch of ints, or an array called windSpeed that contains a bunch of doubles, or an array called favCharacters that contains a bunch of chars.

There are a couple of "rules" you need to remember when dealing with arrays in C++.

First, arrays can only store values of one specific type, so you can't store both cats and dogs in the same array. Sometimes you can "bend" this rule, depending on type compatibility and coercion (e.g., you can store both ints and doubles in an array of type double), but typically you don't do this. Here's an example of an array of characters.

char lettersInAlphabet[26]; // rule1: can only store char values

Second, arrays have a "fixed size". This means that you must tell the computer how many elements you intend to store in an array when you declare said array, and you can never store more than that number of items in the array.

char lettersInAlphabet[26]; // rule2: can only store 26 values

Why does the machine need to know how many elements you intend to store in the array? In a nutshell, the machine needs to know in order to allocate enough memory for N pieces of data of a given type. In the example above, the machine needs to allocate enough memory to store 26 char values.

Third, you need to remember that arrays are "zero-indexed" meaning the first item in the array is "item 0" and the second is "item 1" and so on. This is important to remember, because it is easy to confuse the size of the array with the last index of the array. If you initialize an array like this:

int shotsOfWheatgrassDrunkThisWeek[7]; // rule3: what are the valid indices? 0 through 6.

Notice how the size of the array is 7, but the last index is 6.

C++ Array Syntax

You should have seen some examples of array syntax using [ and ] in class and in your zyBook activities. As such, we won't go over the syntex in detail here. However, here's a brief summary.

int x = 1;
int y = 2;
int z;
int scores[10];
scores[1] = 27;
scores[y] = 2;
z = scores[x] + scores[y];
cout << scores[x + 1];

Please pause here until you totally understand what the syntax means in the example above. How many numbers can score hold? 10. What are their "names"? scores[0] through scores[9]. What is the ending value of z? 29. What is printed to the screen? 2. What does the array look like in memory?

0	1	2	3	4	5	6	7	8	9
	27	2

We suggest you review your section's lecture and zyBook reading, and come see us if you do not understand the syntax in the previous example.

Arrays and Loops

Since you're aware of how to use loops and since you now know how to create arrays, you should recognize that there is a lot of hidden "power" in combining these two elements together. In fact, loops and arrays work so well together, it's rare you'll see one without the other -- they're best friends (but only friends, mind you). Let's take a look:

Or better yet,

const int DAYS_IN_WEEK = 7;

int shotsOfWheatgrass[DAYS_IN_WEEK] = {0, 1, 1, 1, 1, 7, 5};

for (int i = 0; i < DAYS_IN_WEEK; ++i) {
    cout << "On day " << i << " I drank " << shotsOfWheatgrass[i];
    if (shotsOfWheatgrass[i] == 1) {
        cout << " shot." << endl;
    } else {
        cout << " shots." << endl;
    }
}

Do you see how inside the loop, the value for i is used to access each value in the array?

Instructions

Create a program that prompts the users for five whole numbers, stores them in an array, determines which number is the biggest in the array, and then prints the biggest number to the screen. An example interaction follows:

Hey! Witness my first array mojo!
Enter 5 numbers and I will tell you which is the largest.
Number 1: 8
Number 2: 6
Number 3: 7
Number 4: 5
Number 5: 3
So awesome!
The largest number was 8.

If you are unsure how to get started, here are the suggested steps:

Step 1: declare an array of five integers (which you access with 0 to 4).
Step 2: using a for loop, prompt the user for each number and then assign the entered number to the ith value in the array.
Step 3: declare a variable for the largest number, and initialize it to be the 1st value in the array.
Step 4: using a 2nd for loop, read each array value and update the largest number variable (if appropriate). Think carefully about which two values you need to compare.
Step 5: print out the largest number.

This Lab should be submitted with Homework 07