Arrays

Arrays

One-Dimensionalinitialize & display

Arrays as Arguments

Part I

Data Types

a simple or atomic

a structured

* *

char, int, float, double

array, struct, union, class

Structured Data Type - Array

An array is a collection of data storage locations, each of which holds the same type of data. Each storage location is called an element of the array.

An homogeneous aggregate of elements

Each element is referred to as an indexed or subscripted variable.

Array Declaration

SyntaxdataType arrayName [[ ConstIntExpression ]]

The number of elements in an array is stated within square brackets, [ ][ ].

Examplesdouble angle [4]; const int POLY = 8;int testScore [12]; double angle [POLY]; char password [8];

Array Storage

Each array has sufficient memory reserved to hold the number of data items of the given type.

Initializing an array sets up the address of the first element. Addresses of all other elements are offsets from the starting address.

Array elements occupy contiguous memory locations.

Array Element Access

Syntax

arrayName [ indexExpression ]

Program access to each of the array elements is by referring to an offset from the array name. Array elements are counted beginning with zero.

A[0] => add zero to the address of A (1st element)

A[3] => add (3 * width of element) to the address of A (4th element)

Array Element Access

double angle[4]; // declaration

Exampleangle [0] = 6.21;angle [1] = 15.89;angle [2] = 7.5;angle [3] = -45.7;

angle sub zero = 6.21angle sub one = 15.89angle sub two = 7.5angle sub three = -45.7

* * *

6.21

15.89

7.5

-45.7

angle3

--Mathematical notation

Using Array Elements

a write the contents of an array element:cout << angle[2]; // the third element

a assign values to an array element:cin >> angle[3]; // the fourth element angle[2] = pow(axis,4); // the third element

a use it as a parameter:y = sqrt(angle[0]); // the first element

a use it in an expression:x = 2.5 * angle[1] + 64; // the second

element

* * * *

Declare an Array

float myArray[100];

Want to reset myArray to zerosmyArray = 0.0; // works in some languages

In C++, the array name is a pointer to an address in memory

myArray is an address in memory

An attempt to assign a float to a pointer to a float

Array Component Access

for(indexindex=0; index index < arraySize; indexindex++)myArray[indexindex] = 0.0;

100

* *

Zero out an entire array. (Initialize every element to 0.0.)

For loops were “made for” arrays

You always know how many times the loop will execute – once for each element

Off Set

memoryaddresses

starting address

off set by one unit

off set by two units

off set by three units

[ 0 ]

[ 1 ]

[ 2 ]

[ 3]

@#$

@#$

angle int angle[4];

Out-of-Bounds Array Index

memoryaddresses

angle[4] = 135;

cout << angle[5];

[ 0 ]

[ 1 ]

[ 2 ]

[ 3]

@#$

@#$

angle

grade

score

Overwrites value in memory without warning!

Declare an Array

Syntaxtype arrayName[index];

Exampledouble dailyHigh[31] ;

int quizGrade[29] ;

char YSUID[9] ;

*

Initialize an Array Element

SyntaxarrayName[index] = value;

ExampledailyHigh[18] = 16.7;

quizGrade[2] = 15;

YSUID[3] = ‘7’;

*

Initialize an Array at Declaration Time

double angle[4] = {16.21, 15.89, 7.5, -45.7};

double convert[5] = {.64, .89, .76, .83, .65};

int scores[12] = {210, 198, 203, 188, 200, 224, 220, 217, 211, 194, 197, 189};

double iona[8] = {0.0}; // fill with zeros*

Initialize an Array - Variations

int scores[ ] = {210, 198, 203, 188, 200, 224, 220, 217, 211, 194, 197, 189};

char name1[4] = {‘Z’, ‘o’, ‘l’, ‘a’};

char name2[4] = “Zola”; // no braces or ,char phrase [ ] = “Hello World”;

* *

Space for 12 integers

Compiler will allocate 12 bytesWill not compile: “init string too long”

5

Character Arrays - \0

char name1[4] = {‘Z’, ‘o’, ‘l’, ‘a’};

char name2[5] = “Zola”; // no braces or ,needs 5 slots to have space for the end

of string character, \0

char phrase [ ] = “Hello World”;

* *

Compiler will allocate 12 bytes

Sequencing Through an ArrayUse the for statement to sequence through an array.Assume an array with 7 grades in it…Total the contents of an array:

sum = 0;for (index=0; index < 7; index++)

sum += grades[index];

char name1[4] = {‘Z’, ‘o’, ‘l’, ‘a’};Print out an array

for (i = 0, i < 4 , i++) cout << name1[i]; // prints Zola

Loading an Array – with cin

double grade[10];

int index;

for(index=0; index < 10; index++){

cout<<“Enter a grade “;

cin >> grade[index];

}

75 85 65 95 77 88 68 93 59 90

grade0

9

Finding the Max/Min Value

• Set the max or min to element zero.

• Use a for loop to cycle through the array.

• Compare each element to the max/min.

• If necessary, assign a new value to max/min.

How would you do this?

*

Finding the Maximum Value

double find_max(int temp[30]){

int max = temp[0]; //only max seen thus far

for(int index=1; index < 30; index++)if (temp[index] > max)

max = temp[index];return (max);

}

*

If the current temp[ ] is bigger than the max seen thus far. Remember this one!

Finding the Minimum Value

double find_min(int temp[30]){

int min = temp[0]; // minimum thus far

for(int index = 1; index < 30; index++)if (temp[index] << min)

min = temp[index];return ( min );

}

*

Aggregate Assignment - NOT!

There are no aggregate assignments with arrays. That is, you may not assign one array to another.

int x[5] = {11, 22, 33, 44, 55};

int y[5];

y = x; y[ ] = x[ ];

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

y[i] = x[i];

Arrays as Arguments

double find_max(int temp[ ]temp[ ]){

max = temp[0];

for(index = 1; index < 30; index++)if (temp[index] > max)

max = temp[index];return max;

}

double find_max(int temp[ ]temp[ ])

*

Leave blank or use constant

Passing an Array or Elements

find_max(temptemp); // whole array, no [ ]

inventory(priceprice, quantityquantity, amountamount); // 3 arrays

words(cupletcuplet);

find_max(temp[3]temp[3]);

inventory(priceprice, quantity[4]quantity[4], amount[12]amount[12]);

words(cuplet[0]cuplet[0]);

*

Elements of an array

Comparing Arrays as Arguments to Simple Data Types

formal parameterformal parameter formal parameterformal parameterdeclaration fordeclaration for declaration fordeclaration for

parameterparameter Pass-by-ValuePass-by-Value Pass-by-ReferencePass-by-Reference

simple var. int cost int& pricearray impossible int myArray[ ]

array const int source[ ]Keeps function from changing values in the array

Passing an Array Element

Follows the rules for the type of an element in the array

int cntA[1111];cntA[33] is an int and is treated as any

other int when used as an actual argument.

cntA refers to the entire array. It is the address of the array or a pointer to the array.

1-D Array Review

An array is a structured data type

1st element is “arrayName subzero”

Array Declarationint myArray [9];

Array Initializationint myArray [9 ] = { 9, 9, 9, 8, 7, 6, 5, 4,

3};

Array Element ReferencemyArray [3]; // value = 8 *

99

const int MAXELS = 9;

Use everywhere instead of the literal

1-D Array Review

Arrays are always passed by reference, unless const added to the formal parameter.

Array in a Function Prototypevoid myFunction(int [9]);

Array in a Function CallmyFunction(myArray);

Array in a Function Headervoid myFunction(int anyArrayName[9])

optional

Arrays

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