09-arrays

# 09-arrays - COMP 202 COMP 202 Introduction to Computing 1...

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COMP 202 – Introduction to Computing 1 COMP 202 - Arrays 1 COMP 202 Programming With Arrays CONTENTS : • Arrays, 2D Arrays, Multidimensional Arrays • The Array List • Variable Length parameter lists • The For-each Statement Thinking Like A Programmer : Designing for arrays

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COMP 202 – Introduction to Computing 1 COMP 202 - Arrays 2 Part 1 Array Basics
COMP 202 – Introduction to Computing 1 COMP 202 - Arrays 3 Arrays • An array is an ordered list of values 0 1 2 3 4 5 6 7 8 9 79 87 94 82 67 98 87 81 74 91 An array of size N is indexed from zero to N-1 marks The entire array has a single name Each value has a numeric index This array holds 10 values that are indexed from 0 to 9

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COMP 202 – Introduction to Computing 1 COMP 202 - Arrays 4 Arrays A particular value in an array is referenced using the array name followed by the index in brackets For example, the expression System.out.println(marks[2]); refers to the value 94 (which is the 3rd value in the array) That expression represents a place to store a single integer, and can be used wherever an integer variable can For example, it can be assigned a value, printed, or used in a calculation
COMP 202 – Introduction to Computing 1 COMP 202 - Arrays 5 Arrays • An array stores multiple values of the same type – That type can be primitive types or objects – Therefore, we can create an array of integers, or an array of characters, or an array of String objects, etc. • In Java, the array itself is an object – Therefore the name of the array is an object reference variable, and the array itself is instantiated separately

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COMP 202 – Introduction to Computing 1 COMP 202 - Arrays 6 Declaring Arrays The marks array could be declared as follows: int[] marks = new int[10]; Note: – that the type of the array does not specify its size, but each object of that type has a specific size – The type of the variable marks is int[] (an array of integers) – It is set to a new array object that can hold 10 integers
COMP 202 – Introduction to Computing 1 COMP 202 - Arrays 7 Array Object with elements of primitive type (e.g., integer) 0 1 2 3 4 5 6 7 8 9 79 87 94 82 67 98 87 81 74 91 marks

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COMP 202 - Arrays 8 Why Arrays? Imagine you want to write a program that asks the user to enter in 50 student midterm marks. The program would then display each grade with the student’s ID number and then the average for that assignment in a nice report. How would you do it? – One way would be to provide 100 variables: • int mark1, mark2, mark3, (until 50) • int ID1, ID2, ID3, (until 50) – The array provides for a way to create only two variables: • int marks[] = new int[50]; • int IdNumbers[] = new int[50]; – Isn’t this nicer? – Imagine trying to calculate the average with 50 variables…
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## This note was uploaded on 12/29/2010 for the course COMP 202 taught by Professor Verbrugge during the Fall '07 term at McGill.

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09-arrays - COMP 202 COMP 202 Introduction to Computing 1...

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