1 Arrays Chapter 13 Especially read 13.1 – 13.2 Text introduces vectors, which we will not cover,...

1

ArraysChapter 13

Especially read 13.1 – 13.2

Text introduces vectors, which we will not cover, in 13.3

2

Agenda

Arrays – What are they ? Declaring Arrays

Array storage and retrieval

Initializing an array

Using loops to process an array

Array index out of bounds

Passing an array to a function

3

Arrays – What are they ?

A sequence of objects which have the same type

4

Arrays – Think of Lockers

Much like a locker room with lockers of the same size

Each locker is identified by a unique number or an index

5

Arrays – Analogy to Locker Numbers in a Gym

0 1 2 3

Lockers

Locker NumberStuff that’s in the locker

In most programming languages including C, C++ and Java, the first array index would start with 0 and not 1. This is known as zero-based indexing.

The Locker Number is also called the “Index” or “Position”

6

Arrays – Referring to a particular “locker”

The name of the Array as a

whole

This cell is referred to as

lockers[0]

0 1 2 3

Lockers

7

Agenda


Declaring Arrays Array storage and retrieval





8

Declaring an Array of Integers

Declaring an arraytype name-of-array[size-of-array];

Example int myarray[10];

myarray 0 1 2 3 4 5 6 7 8 9

myarray holds 10 integers:

myarray[0] through myarray[9]

9

Defining an array of char

Defining an arraytype name-of-array[size-of-array];

Example char word[6];

word 0 1 2 3 4 5

word holds 6 char data:

word[0] through word[5]

Trivia: this is what

Is called a C-string!

10

Agenda


Declaring Arrays

Array storage and retrieval Initializing an array




11

Array storage and retrieval#include <iostream.h>void main(){float a[3]; a[0] = 55.55;a[1] = 11.11;a[2] = 33.33;cout << “a[0] = “<< a[0] << endl;cout << “a[1] = “<< a[1] << endl;cout << “a[2] = “<< a[2] << endl;

}

55.55

11.11

33.33

0

1

2

a

Put a 55 in first cell

Program Output:

a[0] =55.55

a[1] =11.11

a[2] =33.33Output last cell to console

12

More Array Storage and Retrieval

Each cell of the array is just like a separate variablecin>>a[2]; // input cell 2 of array acout<<a[1];// display cell 1 of array a

cout<<a[0]<<“ “<<a[1]<<“ “<<a[2]<<endl;

a[1]=a[2]; //assign cell2 of a to cell1a[0]=a[1]+a[2]; //put sum of 1 & 2 in 0

File input and output is just as easyinfile>>a[0]>>a[1]>>a[2];

13

Agenda


Declaring Arrays


Initializing an array Using loops to process an array



14

Arrays – Initialization List

When arrays are declared, they contain garbage data

Arrays can be initialized similar to structsfloat a[3] = {22.2, 44.4, 66.6};

22.2

44.4

66.6

0

1

2

a

ONLY AT DECLARATION TIME!

15

Arrays – Initialization List

Arrays of char (C-strings) can be initialized one of two ways:

char word[6] = {‘H’,’e’,’l’,’l’,’o’};

char word[6] = “Hello”;

wordH e l l o \0

Method 2 puts a string terminator symbol (\0) in the array

You should make size one larger than number of letters

Terminator symbol

16

Arrays – Partial InitializingWhen the list is smaller than the size of the array, 0’s are used to fill in remaining cells

float a[6] = { 22.2, 44.4, 66.6};

a

22.2 44.4 66.6 0 0 0

17

Your Turn, IDraw the following arrays

float data[8]={6.2, 3.4, 3.5};

char text[10]=“Albatross”;

int temp[6]={3};

18

Your Turn, IIDraw the following arrays after modifying as shown:

float data[8]={6.2, 3.4, 3.5};

data[6]=data[2];

data[5]=data[2]+data[1];

char text[10]=“Albatross”;

text[1]=text[2]=‘x’;

19

Agenda


Declaring Arrays



Using loops to process an array Array index out of bounds


20

Arrays – Using for loopsFor loops are a more compact way of processing loopsInstead of this:

cin>>a[0];cin>>a[1];cin>>a[2];cin>>a[3];cin>>a[4];cin>>a[5];

You can do this:

for (k=0; k<6; k++)

cin>>a[k];

21

Arrays – Using for loopsAnytime you see a pattern in what you are doing, you can replace it with a for-loop:

Instead of this:

a[0]=a[9];

a[1]=a[8];

a[2]=a[7];

a[3]=a[6];

a[4]=a[5];

You can do this:

for (k=0; k<5; k++)

a[k] = a[9-k];

22

Advantage of for loops

More compact, Saves typing

Easier to modify if size of array changes

Since for loops are so common, a technique of using a const int for size of the array:

const int SIZE=10;

int k, data[SIZE];

for (k=0; k<SIZE; k++) cin>>data[k];

23

Your Turn IIIDraw the following arrays

float k, data[8];

for (k=0; k<8; k++) data[k]=k;

float k, data[8];

for (k=0; k<8; k++) data[k]=k-5;

float k, data[8];

for (k=0; k<8; k++) data[k]=7-k;

24

Agenda


Declaring Arrays




Array index out of bounds Passing an array to a function

25

Arrays – NOTE

Initializing an array with more values than the size of the array would lead to a run-time (not compiler!) error

Referring to an array index larger than the size of the array would lead to a run-time (not compiler!) error

26

Arrays – Index out of bounds

#include <iostream.h>

void main()

{

const int SIZE=4;

float a[SIZE] = { 33.3, 44.4, 55.5, 66.6 };

for (int i=0; i < 7; i++)

cout << "a[" << i << "] = " << a[i] << endl;

}

You can get very weird results!

Slots 4-6 are out of bounds

27

Arrays – Index out of bounds

This would display the entries of the arrayThe last three element displayed are junk since this is not part of the array and is part of memory which are not initializedSometimes you can accidentally modify data that does not belong to your array! Like…another variable!!

28

Agenda


Declaring Arrays






29

Passing an Array to a FunctionWhen passing an array to a function, we need to tell the compiler what the type of the array is and give it a variable name, similar to an array declaration

float a[]

We don’t want to specify the size so function can work with different sized arrays. Size comes in as a second parameter

This would be a parameter in fn header

30

Passing an Array to a Function#include <iostream.h>

void Display(int data[], int N){ int k;cout<<“Array contains”<<endl;for (k=0; k<N; k++)

cout<<data[k]<<“ “;cout<<endl;

}void main() {int a[4] = { 11, 33, 55, 77 }; Display(a, 4);

}

An int array parameter

of unknown size

The size of the array

The array argument, no []

31

Passing an Array to a Function#include <iostream.h>int sum(int data[], int n); //PROTOTYPE

void main() {

int a[] = { 11, 33, 55, 77 }; int size = sizeof(a)/sizeof(int); cout << "sum(a,size) = " << sum(a,size) << endl;

}

int sum(int data[], int n) {

int sum=0; for (int i=0; i<n;i++)

sum += data[i];return sum;

}

An int array parameter

of unknown size

The size of the array

The array argument, no []

32

Arrays are always Pass By Reference

Arrays are automatically passed by reference. Do not use &.

If the function modifies the array, it is also modified in the calling environment

void Zero(int arr[], int N)

{

for (int k=0; k<N; k++) arr[k]=0;

}

33

Your Turn

Add function calls to Zero out the array below, and Display it:

int samples[10000];

// your call to Zero here:

// your call to Display here:

34

That’s a wrap !

What we learned today:What are arrays

Array indexing

Array initialization

Array index out of bound error

Passing arrays to functions

1 Arrays Chapter 13 Especially read 13.1 – 13.2 Text introduces vectors, which we will not cover,...

Documents

Transcript of 1 Arrays Chapter 13 Especially read 13.1 – 13.2 Text introduces vectors, which we will not cover,...