1. Module 5 Working with Arrays

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What is an array?
Data structure
a collection of elements
Ordered
first, second, third, …
Homogenous
all elements are the same type
Fixed Size
defined when your code compiles
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Declaring Arrays
type name[ size ];
int grades[ 6 ];
Use named constant for array size
#define MAX_GRADES 6
int grades[MAX_GRADES]; 1 2 3 4 5
???
grades:
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Initializing Arrays
int scores[5] = {99, 44, 22, 11, 10}; 1 2 3 4 99 44 22 11 10
scores:
char word [ ] = {‘B’, ‘o’, ‘b’}; 1 2
‘B’
‘o’
word:
double costs[5] = {5.45, 7.89, 1.01}; 1 2 3 4
5.45
7.89
1.01
costs:
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5. Accessing Array Elements
array_name[ index ]
First element has index = 0
Max index for an array with N elements is N – 1
int cats[MAX_CATS] = {2, 4, 6, 8, 10, 12};
int nrCats = cats[4];
cats[5] = cats[5] – cats[0] + 6;
printf(“ %d\n”, cats[1]);
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Out of Bounds
int ages[4] = {12, 24, 36, 48};
ages 1 2 3
??? 12 24 36 48
int myAge = ages[5];
ages[-2] = 14;
Compiler does not check validity of index
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For Loops and Arrays
#define MAX_CATS 6 int i, cats[MAX_CATS]; for(i = 0; i < MAX_CATS; i++) { cats[i] = 0; } for(i = MAX_CATS-1; i >= 0; i--) { printf(“%d\n”, cats[i]); } // displays backwards
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const Qualifier
Specified that an initialized variable won’t change values
const double pi = ;
const char digits[ ] = {
‘0’, ‘1’, ‘2’, ‘3’, ‘4’,
‘5’, ‘6’, ‘7’, ‘8’, ‘9’ };
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Let’s take a look
CB – arrays1
Note the use of #define for array sizes – if array size changes, just change #define in one place
IDOM.. i = 0; i < size; i++
CB-Program7.2 (counting responses)
Initialization with a for-loop
Not using [0] to avoid i-1 coding
CB-Program7.3 (calc and store Fibonacci)
Discuss the rabbit story (text)
No need to initialize entire array
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Exercises
30 mins
From text, pg 118
#4 and 5
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11. Entering values into an array
First need to declare the array
Use a for loop to
ask for values
Enter value
Still uses same scanf setup
Use another for loop to
Display values enter
DOES NOT USE SAME printf!!
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12. Entering values into an array
int scores[10];
for(int i = 0; i < 10; i++) {
printf("Please enter the score: ");
scanf("%d", &scores[i]); }
printf("\nThese are the scores you entered:\n ");
printf("%d\n", scores[i]);
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13. Partially Filled Arrays
Capacity (size) determined by declaration
Program must track number of actual elements
int studentGrades[ 10 ];
int nrGrades = ; 4 3 1 2 1 2 3 4 5 6 7 8 9 34 22 99 88
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Let’s take a look
CB – PartialArrays
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15. Fundamental Array Operations
Search
Does the array contain a specified element?
Sort
Arrange the array elements in order from low to high (or high to low)
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Linear Search
Examine elements of the array starting at the first element until
The target element is found – SUCCESS
There are no more elements – FAILURE
Use a while-loop with a compound conditional
Check if target was found
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17. Linear Search Progression
Search for 39 1 2 3 4 5 6 7 8 9 20 12 87 44 39 6 45 22 68 77
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Exchange Sort
Compare the first element with all other elements. If the other element is smaller, exchange it with the first element.
The first element is now the smallest
Compare the second element with all other elements (except the first). If the other element is smaller, exchange it with the second element.
The second element is now the second smallest
Compare the third element with all other elements (except the first and second). If the other element is smaller, exchange it with the third element.
The second element is now the third smallest
. . .
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19. Exchange Sort Progression
First Pass Second Pass Third Pass More Passes…
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Let’s take a look
C::B – Exchange sort
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Binary Search
Fast search for specified target element
Requires sorted array
Algorithm
Look at the middle element
If the middle element is the target, stop
If the target > middle element, look at the middle element of the upper “subarray”
If the target < middle element, look at the middle element of the lower“subarray”
Continue until found or all elements examined
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Binary Search
Videos
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23. Binary Search Progression
Search For 68 1 2 3 4 5 6 7 8 9 5 12 16 23 36 44 45 56 68 77
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Let’s take a look
C::B – BinarySearch
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Exercises
From the Text -- pg 117
#3 – Modify program 7.2 (do NOT use break) --
#4 – calc average of 10 floating point values- AM
“hard code” values into an array of size 10
#5 – predict output, the code and verify - AM
Ex1-HighestQuiz.docx
Ex2-Sets.docx
Ex3-SieveOfE.docs (see text #7)
Ex7-PartialArrays
Rewrite program7-4.c using a while-loop
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