introduction to array 20082013 - student

7/29/2019 Introduction to Array 20082013 - Student

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Introduction to Array


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Properties of array Index

Data type

Contiguous One dimensional array

Operations using arrayMinimum

Maximum Count

Average

Summation

Array


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What is Array?

A block of memory locations in the internalmemory that is assigned to one variable name.

Each array memory location is called element.

Sometimes called a subscripted variable.

Static arrays An array in which the maximum number of

elements cannot change during processing

Dynamic arrays

An array in which the maximum number ofelements can change during processing

More flexible and use less memory space thanstatic arrays, but.. more time consuming during

processing


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Array

A series of elements of the same type placed in contiguous memory

locations that can be individually referenced by adding an index to a

unique identifier.

Example:

To store 5 values of type in tin an array without having to declare 5different variables, each one with a different identifier.

To store 5 different values of the same type, in tfor example, with a

unique identifier.

For example, an array to contain 5 integer values of type int called

billy could be represented like this:


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Array

Each blank panel represents an element of the array, in this case

integer values of type int.

These elements are numbered from 0 to 4 since in arrays the first

index is always 0, independently of its length.

Like a regular variable, an array must be declared before it is used.A typical declaration for an array in C++ is:

type name [elements];

where type is a valid type (like int, float...), name is a valid identifier

and the elements field (which is always enclosed in square brackets

[]), specifies how many of these elements the array has to contain.


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Base-Zero vs Base-One Arrays

Base-zero system:

A computer system in which array element numbers begin with zero

rather than one

Base-one system:

A computer system in which array element numbers begin with one

rather than zero


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Base-Zero vs Base-One Arrays

0

1

2

3

4

5

6

7

N

A[0]

A[1]

A[2]

A[3]

A[4]

A[5]

A[6]

A[7]

...

A[N]

Base 0

A

1

2

3

4

5

6

7

8

N

A[1]

A[2]

A[3]

A[4]

A[5]

A[6]

A[7]

A[8]

...

A[N]

Base 1

A


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Base-Zero Array

Example:

100 list of marks of integer type, will be declared as:

int mark1, mark2, mark3, , mark100;

Notes:

If we have 100 marks to be stored, you can imagine how long we

have to write the declaration part by using normal variable

declaration?

By using an array, it can be declared as: int mark[100];

This will reserve 100 contiguous/sequential memory locations for

storing the integer data type.

Graphically can be depicted as follows:


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Base-Zero Array (Cont)


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Types of array

Three types

One-dimensional array

Two-dimensional array

Multidimensional array


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The simplest array structure

Consists of one column of memory locations.

Dimension refers to the array size that is how big the

array is. A single dimensional array declaration has the

following form:

array_element_data_typearray_name[array_size];

array_element_data_type: declares the base type ofthe array, which is the type of each element in the

array.

array_name: is any valid C++ identifier name.

array_size: defines how many elements the array will


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Example:

To declare an array of 20

characters, named

character: char character[20]

Can be depicted as

follows:

The array character can store up to 20 characters with the

first character occupying location character[0] and the last

character occupying character[19].

Note that the index runs from 0 to 19.

An index always starts from 0 and ends with (array size-1).


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Eg: One-dimensional array named

Age

Age[0]

Age[1]

Age[2]

Age[3]

Age[4]

Age[5]

Age[6]

Age[7]

Age[8]

Age[9]

0

1

2

3

4

5

6

7

8

9

32

54

25

36

45

20

28

50

42

20

Array

Age

VariableReference Name

The number inthe parentheses

refers to the box

number in the

array, the element

number

Fifth element of

theAge array

Age[4] = 45

The index of the first

position in an array is 0.

Pronounced:

Age-sub-4


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Array Initialization

An array may be initialized at the time of itsdeclaration, which means to give initial values to anarray.

Initialization of an array may takes the following form:

type array_name[size] = {value_list};

For examples:

int id[7] = {1, 2, 3, 4, 5, 6, 7};

Declares an integer array id and it immediately assigns the

values 1, 2, 3, , 7 to id[0], id[1], id[2],, id[6].

float x[5] = {5.6, 5.7, 5.8, 5.9, 6.1};

Assigns the values 5.6 to x[0], 5.7 to x[1], and so on.


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Array Initialization

charvowel[6] = {a, e, i, o, u, \0};

Assigns the characters a to vowel[0], e tovowel[1], and so on.

The last character in the array vowel is the NULLcharacter (\0).

charvowel[6] = "aeiou";

When the value assigned to a character array is astring, the compiler automatically supplies theNULL character but we still have to reserve oneextra place for the NULL.


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Exercise 1

1. How many slots/indexes does this array have?

2. How many characters, counting the null character at the end, does

this array hold?

3. The number of an index is also called an index. What is the lowest

index?

Answers:

1. 11

2. 7 characters including the null character3. 0

0 1 2 3 4 5 6 7 8 9 10

L o v i n g \0


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Exercise 1

4. What is the highest index for this array?

5. Is the number for the highest index the same as that for the number ofindexes?

6. What is stored in the last index as a character, that is, in an indexnumber 5?

7. What is stored in the last index numerically? All strings should have thisnull character stored in its last index to signal the end of the string.

Answers:

4. 10

5. No. The number of indexes are 11 but the highest index is 10 because

the index counting starts from 0 instead of 1.

6. A 'g' character.

7. A null character.0 1 2 3 4 5 6 7 8 9 10

L o v i n g \0


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Reminder!

null characteris used to terminate a

string and this is specific to string only


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Exercise 2

1. Draw and name a one-dimensional array that would hold 10

temperatures. Number the elements.


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Answer 2

0 1 2 3 4 5 6 7 8 9

temperatur

es


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Exercise 3

Given an array called myArraydeclared with 10 items, or boxes from [0] to

[9],

which of the following designations would be legal calls? Assume X = 5.

1. myArray[X]

2. myArray[2*X]3. myArray[0]

4. myArray[X-6]

5. myArray[4*X]


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Answer 3

1. myArray[5]

2. myArray[10]

3. myArray[0]

4. myArray[-1]

5. myArray[20]

1. Legal because there is a box

5

2. Illegal because there is nobox 10

3. Legal because there is a box

0

4. Illegal because there is no

box -1


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Operation using array

Summation

Average

MinimumMaximum

Count


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Summation

Example: Create a pseudocode that read 3

floats into an array and print their sum.

Problem: Read and add 3 float numbers in an

array Input: Float numbers

Output: Sum of numbers in array


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Summation 1

Start

float data[3]; int i;

Set sum = 0;

Promt for data.

for (i=0; i


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Summation 2

Start

int i, total = 0, y[n] = {6,9,2,4,5,23,12};

for (i=0; i


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Average

Example: Input 10 integers. Determine and

display the mean (average) integers.

Problem: Read and add 10 integer numbers in an

array Input: Integer numbers

Output: Average of numbers in array


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Average

Start

int data[10], count; float average;

Set sum = 0;

Promt for data.

for (count=0; count


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Minimum

Start

int i; float small, a[n]={100.00,40.00,-

30.00,400.00,60.00,-25.00,-24.00,0.00,3.24,0.50};

Set small = a[0];

for (i=0; i


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Maximum

Start

int a[5] = {3, 7, 4, 9, 6}, i;Set largest = a[0];

for (i=0; i largest)

largest = a[i]

Endfor

Print largest

End

Example: Printing the largest number in the

array


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Maximum (Cont)

Start

int a[5] = {3, 7, 4, 9, 6}, i;

Set largest = a[0];

Set index = 0;

for (i=0; i largest)

largest = a[i]

index = i

Endfor

Print index

End

Example: Print only the index of the largest

number in the array


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Count

Example:

Initialize an array with 6 integers. Read another integer and

print the value of each array element that is less than this

read-in integer and print the number of elements that were

not printed. For example, if the array were 40, 80, 20, 50,90, 30 and an 80 were read in, then the output would be

something like:

-------Output-------

40 20 50 30

count = 2


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Count

Start

int num[6] = {40, 80, 20, 50, 90, 30}, num2, i,

count=0;

Prompt for an integer num2Read integer num2

for(i=0;i num2)

count = count + 1

Endfor

Print count

End


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Exercise 1

1. Initialize an array with 6 integers for thefollowing array arr. Read another integer andadd that number to each element in the array.Print the original and the new array element.

arr [6] = {3, 5, 7, 2, 12, 10}


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Exercise 2

1. Print the sum of the numbers greater than 5and the count of the elements less than orequal to 5 in the following array:

a[5] = {3, 7, 4, 9, 6},

sum = 22, count = 2

introduction to array 20082013 - student

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