arrays week 9

8/16/2019 Arrays Week 9

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ITEC102- SIBT

Lecture 9

Week 9

Arrays


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Last Week

• Functions

• Nested Function Calls

• Global and Local Variables to Functions

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This Week

• Arrays

– Declaration

– Initialization

– Indexing

– Passing

• Practice and Exercises



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Recap

• Consider the following code

int test(int a, int b){

return a*b-b+a;

}

• Trace out the output of the following function

call

print(test(test(test(2,1),test(1,2)),test(test(3,3),3)));

• 137



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Need for Arrays

• To store a set of values of the same data type

• luckyNumbers = {80,6,12,2001,25,17,2011};

• favMovies = {”brave heart”, ”gladiator"};

• fascinatingValues = {3.14159, 42, 1.618};

• lowerCaseVowels ={'a','e','i','o','u’};

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Need of Arrays

• Without Arraysint x1 = 5;

int x2 = 10;

//AND SO ON !!

int x500 = 2500;

• With Arrays

int[] x = new int[500];for(int i=0; i


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Array Declaration

• SyntaxdataType[ ] arrayName;

• Examples – • int[ ] ages;

• float[ ] salaryList;

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Array Instantiation

• You need to allocate memory for the items in

the array before you can use it.

arrayName = new dataType[size];

• Examples –

ages = new int[5];

wages = new double[24];

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Instantiation Implications

• int[ ] ages;

• ages = new int[5];

ages

ages[0] = 0

ages[1] = 0

ages[2] = 0

ages[3] = 0

ages[4] = 0

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Declaration and Instantiation

• dataType[] arrayName = new dataType[size];

• Examples – • int[ ] ages= new int[50];

• double[ ] wages = new double[24];

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Sample Questions

• Declaration int[] ages;

• Instantiation ages = new int[5];

• Declare, instantiate arrays for following requirements.

• Draw the memory diagram.

a. 10 integers

b. 5 floating point values

c. 8 charactersd. 4 booleans

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ages

ages[0] = 0

ages[1] = 0

ages[2] = 0

ages[3] = 0

ages[4] = 0



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Solutions – Sample Questions

a. 10 integers:• int[ ] intArr = new int[10];

b. 5 floats:

• float[ ] floatArr = new float[5];

c. 8 chars:• char[ ] charArr = new char[8];

d. 4 booleans:

• boolean[ ] boolArr = new boolean[4];

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Getting number of items

• arrayName.length

• Example, – int [ ] ageList = new int [6];

– println(ageList.length); //6

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Accessing Array Items

• float[ ] arr = new float[5];

• Access item at index 0 arr[0]


• Access item at index 2 arr[2]• Access item at index 3 arr[3]


• ---------------------------• Access item at index i arr[i]• for i from 0 to arr.length - 1

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Accessing Array Items

• //for each item of the array

• for(int i=0; i


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Initialization by Iteration

• float[] arr = new float[30];


• for(int i=0; i


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Explicit Initialization

• When you already know the values you want

inside the array, and the number of items is

not too large – • dataType[] arrayName = {val1, val2, … };

• Example –

• int[] gradeBounds = {50, 65, 75, 85};• char [ ] lowerCaseVowels = {'a’,'e’,'i’,'o’,'u'};

• float[ ] marathonDistances = {21.0975, 42.195};

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Display by Iteration


• for(int i=0; i


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Operating on Array Items

float[] GPAs = new float[10];

float total= 0, avgGPA;

for(int i=0; i


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Class Exercise

• int[] arr = new int[10];

for(int i=0; i


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Class Exercise


• for(int i=0; i


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Problem Solving

• Create an array that contains 100 integers

such that the

• first item is 0

• second item is 5

• third item is 0

• fourth item is 5• And so on…

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Problem solving

• First, creating an array to hold 100 integers

int[] arr = new int[100];

• arr [0] should be 0• arr [1] should be 5

• arr [2] should be 0

• arr [3] should be 5• arr [4] should be 0

• arr [5] should be 5

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Problem solving

• even indexed values are 0, odd indexed values are 5

• declare and allocate memory for array arr to store 100ints

• for each item indexed by i (i = 0 to arr.length-1)• if i is even

• arr[i] = 0

• else

• arr[i] = 5

• end of if

• end of for

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Problem solving

• even indexed values are 0, odd indexed values are 5


• for(int i = 0; i < arr.length; i++) {

• if ( i % 2 == 0 ) {• arr[i] = 0;

• }

• else {

• arr[i] = 5;• }

• }

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Class Exercise

• Assuming the following array

int[ ] nums = {5,4,2,7,6,8,5,2,8,14};

Write a code to square each number in array

((i.e., multiply each by itself)

• for (int i = 0; i < nums.length; i++) {

nums[i] = nums[i]*nums[i];}



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Class Exercise


int[ ] nums = {5,4,2,7,6,8,5,2,8,14};

Write a code to calculate the sum of all the

numbers.

• int sum = 0;

for (int i = 0; i < nums.length; i++) {

sum += nums[i];}



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Class Exercise


int[ ] nums = {5,4,2,7,6,8,5,2,8,14};

Write a code add a random number between

zero and 10 to each number.

• for (int i = 0; i < nums.length; i++) {

nums[i] += int(random(10));

}



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Class Exercise


int[ ] nums = {5,4,2,7,6,8,5,2,8,14};

Write a code to add to each number the

number that follows in the array. Skip the lastvalue in the array.

• for (int i = 0; i < nums.length-1; i++) {

nums[i] += nums[i+1];}



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Passing array to functions

void initialize(int[] a, int low, int high) {

for(int i=0; i


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Passing Array to Functions

• So, when you pass an array (say A) to a

function as array (B), and modify B, A is

modified too.

• This is, because, unlike individual

variables, a duplicate of an array is NOT

made and the formal parameter (B) is

physically the same as A

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Passing Array to Functions

A = 10

B = 10

10

20

30

A and B being

individual variables

A and B being

arrays

A,B

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Declaring Multiple Arrays

• float[] x, y;

• x = new float[4];

• y = new float[4]; //Error

• Because the declaration code is parsed as:

• float[] x;

• float y;

• You need to declare each array individually as:

• float[] x;

• float[] y;

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arrays week 9

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