Chapter 6 Arrays
ITP 134 C++ Study Guide
Chapter 6 Arrays
Instructions: Use this Study Guide to help you understand the important points of this chapter. See
the book for lots of great programming examples. Important concepts, keywords, statements and
functions are shown in emphasized font.
Code syntax and examples are shown in code font.
Games & Graphics in C++
2nd edition by Tony Gaddis
6.1 Array Basics
CONCEPT: An array allows you to store a group of items of the same data type together in memory. Processing a large of
items in an array is usually easier than processing a large of items stored in separate variables. (pg 205)
Arrays use a single variable name to store a group of values. Arrays are specifically designed to store and process data.
(pg 205)
Variables are a named memory location and can only hold one value at a time. (earlier chapters)
Array Elements and Subscripts
 The storage locations in an array are known as elements. In memory, an array’s elements are located in
consecutive memory locations. (pg 207)
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Each element in an array is assigned a unique number known as a subscript or index. In C++, the first subscript
is 0. (pg 207)
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You must declare what datatype the array can store. Every element in the array has to be the same datatype
such as int, float, bool etc.
By Eaton
For example, suppose you are writing a program to calculate the average of 5 numbers. Using variables you
could write the following code snippet.
int size, number0, number1, number2, number3, number4, sum, average;
const SIZE = 5;
// how many numbers are you averaging?
number0 = 10;
// numbers start at 10 and increment 10
number1 = 20;
number2 = 30;
number3 = 40;
number5 = 50;
sum = number0 + number1 + number2 + number3 + number4;
average= sum / size;
This doesn’t seem so bad, but suppose you had to average 20 numbers. You can easily see the limitations of
using simple variables. Let’s rewrite this code using an array of 20 numbers and a for loop.
const SIZE = 20;
int number[size];
for (int i = 0; i < size; i++)
{
number[i]= 10*(number[i]+1);
Sum += number[i];
}
average = sum/size;
ITP 134 – Mrs. Eaton
Chapter 6 Study Guide – 2nd Edition
Page 1
Chapter 6 Arrays
See Program 6-8 AverageArray.cpp (pg 224) for another
code example of averaging numbers.
the array. (pg 216) See Figure 6-4 Sequential search
logic for a flowchart of this process.
See Figure 6-2 for a visual example of values stored in
an array. (pg 208)
Searching a String Array
Program 6-4 StringSearch.cpp demonstrates how to use
the sequential search algorithm to find a target number
in an array. (pg 219)
Inputting and Outputting Array Contents
You can read values from the keyboard and store in
array just as a regular variable. You can also print the
contents of an array element. (pg 208)
Array Initialization
Shortcut: You can initialize an array when you declare it.
Here is an example (pg 209):
const int SIZE = 5;
int numbers[SIZE} = { 10, 20, 30, 40, 50 };
Using a Loop to Step through an Array
Video Note (pg 210) See the code snippet for another
example of using a for loop with an array . Also see my
example on page 1 of this study guide.
No Array Bounds Checking in C++
The C++ language does not check to see if you are out
of bounds for the subscripts of any arrays that you
create. You need to be sure to remember that the array
subscripts start at 0 and the last subscript is always one
less than the number of items that the array can hold.
You will get an “out of bounds” error message or your
program will crash if your program has this logic error.
(pg 213)
Watch for Off-by One Errors
A common mistake is off-by-one-error. Since humans
count from 1 instead of 0 it is easy to do. You need to
be sure to remember that the array subscripts start at 0
and the last subscript is always one less than the
number of items that the array can hold. (pg 213)
Processing the Elements of an Array
You can use the elements in an array for processing
with mathematical expressions just as you can with
variables. See In The Spotlight: Using Array Elements
in a Math Expression for an example. (pg 214 – 215)
6.2 Sequentially Searching an Array
CONCEPT: The sequential search algorithm is a simple
technique for finding an item in an array. It steps
through the array, beginning at the first element, and
compares each element to the target item. The search
stops when the element is found or reach the end of
ITP 134 – Mrs. Eaton
6.3 Processing the Contents of an Array
Copying an Array
You can copy the contents of one array to another using
a loop. For example: (pg 221)
const int SIZE = 5;
int numbers1[SIZE} = {100, 200, 300, 400,
500);
int numbers2[SIZE];
//copy values from numbers1 array into
//numbers2 array
for (int i=0; i < SIZE; i++)
{
numbers2[i] = numbers1[i];
}
Implicit Array Sizing
In C++, you can declare an array and initialize an array
without specifying its size. (pg 484)
For example:
int numbers[ ] = { 2, 4, 6, 8, 10 };
// array will be size 5
Comparing Arrays
If you need to compare two arrays to see if they are
equivalent, then you need to use a loop that goes
through all the elements and compares each value for
both arrays. See the code snippet example (pg 221).
Totaling the Values in an Array
To total the values in a numeric array, you use a loop
with an accumulator variable. See Program 6-7
TotalArray.cpp for an example. (pg 223)
Averaging the Values in an Array
To calculate the average of the values in a numeric
array, the first step is to use a loop with an accumulator
variable. The second step is to divide the sum by the
number of elements in the array. See Program 6-8
AverageArray.cpp for an example. (pg 224)
Chapter 6 Study Guide – 2nd Edition
Page 2
Chapter 6 Arrays
Finding the Highest and Lowest Values in an
Array
To find the highest value in an array, create a variable to
hold the highest value. Then assign the value in array[0]
to this variable. Loop through the array element to
compare the next value to the current highest element.
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See Figure 6-5 for a flowchart example to find
the highest value. (pg 225)
See Program 6-9 HighestElement.cpp for an
example. (pg 226)
See Figure 6-6 for a flowchart example to find
the lowest value (pg 227)
See Program 6-10 LowestElement.cpp for an
example. (pg 227-228)
Passing an Array as an Argument to a Function
You can pass an entire array as an argument to a
function, which give you the ability to modularize many
of the operations you can perform with an array.
Typically you pass the array and then the size of the
array.

See Program 6-11 ArrayArgument.cpp for an
example. (pg 229)
Partially Filled Arrays
Sometimes you need to store a series of items in an
array, but you do not know the exact number of items.
One solution is to make the array large enough to hold
the largest possible number of items. If you only
partially fill an array you need to keep track of how
many items are currently stored in the array so you do
not try to process an empty item in the array. (pg 230)

See Program 6-12 PartiallyFilledArray.cpp for an
example. (pg 231-232)
From CSC 200 Intro to CS class
CONCEPT: A sorting algorithm rearranges the contents
of an array so they appear in a specific order. The
selection sort is a specific example of a sorting
algorithm.
6.5 Two-Dimensional Arrays
CONCEPT: A two-dimensional array is like several
identical arrays put together. It is useful for storing
multiple sets of data.
Remember the subscripts are array[row][column]

Passing Two-Dimensional Arrays to Functions
When a two-dimensional array is passed to a function,
the parameter type must contain a size declaratory for
the number of columns in addition to the number of
rows.
 See Program 6-16 Pass2dArray.cpp for an
example. (pg 244-245)
6.6 Arrays of Three or More
Dimensions
CONCEPT: To model data that occurs in multiple sets
(such as GPS data) most languages allow you to create
arrays with multiple dimensions.
See Figure 6-12 for a visual representation of a 3D array.
(pg 246)
Chapter 6 Program Examples
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6.4 Parallel Arrays
CONCEPT: By using the same subscript, you can
establish relationships between data stored in two or
more arrays.
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See Program 6-14 ParallelArrays.cpp for an
example. (pg 238-239)
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ITP 134 – Mrs. Eaton
See Program 6-15 TwoDimensionalArray.cpp for
an example. (pg 242-243)
Chapter 6 Study Guide – 2nd Edition
Program 4-1 Comissions.cpp (pg 134-135)
Program 6-1 ArrayInputOutput.cpp (pg 208-9)
Program 6-2 ArrayLoop.cpp (pg 211-212)
In the Spotlight:
Program 6-3 CoffeShopPayroll.cpp (pg 214-215 )
Program 6-4 SequentialSearch.cpp (pg 218 )
Program 6-5 StringSearch.cpp (pg 219-220 )
Program 6-6 CompareArrays.cpp (pg 221-222 )
Program 6-7 TotalArray.cpp (pg 223 )
Program 6-8 AverageArray.cpp (pg 224 )
Program 6-9 HighestElement.cpp (pg 226)
Program 6-10 LowestElement.cpp (pg 227-228 )
Program 6-11 ArrayArgument.cpp (pg 229)
Program 6-12 PartiallyFilledArray .cpp (pg 231232 )
In the Spotlight:Program 6-13 main function (pg
233-234 )
Program 6-13 getTestScores function(pg 235)
Program 6-13 getTotal function(pg 236)
Program 6-13 getLowest function(pg 236)
Program 6-14 ParallelArrays .cpp (pg 238-239 )
Program 6-15 TwoDimensionalArray .cpp (pg
242-243 )
Program 6-16 Pass2dArray .cpp (pg 244-245)
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