Why do we need Arrays int main What do we do if we have to store more than 1 piece of information of the same type int item0 item1 item2 int sum Topic 4 Arrays We declare different variables cout Enter 3 integers cin item0 item1 item2 Chapter 8 in the shrinkwrap Chapter 9 in Malik sum item0 item1 item2 cout The sum of the numbers sum endl cout the numbers in reverse order are cout item2 item1 item0 endl return 0 Topic 4 ch 8 Arrays What are arrays Simple Composite data types A collection of data of the same type A special group of variables Simple Data Types Data types that store only one piece of information What we have been using thus far Int float double char long Arrays can hold many pieces of data all have the same data type and name but different values 2 Structured Composite Data types Each data item is a collection of other data items Aggregate data type Means grouping Used for lists of like items Test scores temperatures names etc Avoids declaring multiple simple variables Can manipulate list as one entity Topic 4 ch 8 Arrays 3 Topic 4 ch 8 Arrays 4 Declaring an Array Now on to Arrays Syntax dataType arrayName number of elements Declaring an array allocates the memory for the array Example int scoresAr 5 declares an array of 5 integers named score The number of elements can be a literal e g 5 int scoresAr 5 Or a named constant const int NUMBER OF TESTS 5 int scoresAr NUMBER OF TESTS 6 Topic 4 ch 8 Arrays 1 Elements and Indexes Memory and Arrays 4 bytes Each individual item in an array is called an element Each element has an index associated with it An index is a number which indicates which value we are referring to Example scoresAr 0 the first element in our array scoresAr 0 scoresAr 1 scoresAr 2 scoresAr 3 scoresAr 4 scoresAr 5 int scoresAr 5 Index The first element is ALWAYS zero So if we have 5 elements our indexes would be 0 1 2 3 4 or scoresAr 0 scoresAr 1 scoresAr 2 scoresAr 3 score 4 Note The brackets specify the size in the declaration and the subscript Topic 4 ch 8 Arrays or index anywhere else int price price 0 int itemsAr 5 2 12 1 This is not considered good style do not do this in this class please int itemsAr 5 2 12 1 0 0 This is okay int itemsAr 5 0 if you have more values than elements specified then you will get a compiler error int itemsAr 5 2 12 1 2 9 5 compiler error if you don t specify the number of elements it will default to the number of values in the list int itemsAr 2 12 1 2 9 5 children will default to 6 elements Topic 4 ch 8 Arrays Topic 4 ch 8 Arrays Initializing using a FOR loop include iostream h NOTE For Loops are very useful when you need int main to access every element in an array float gpasAr 5 an array holding 5 grade point averages INP OUT load the array from the keyboard This is not recommended Example Do a desk check with Inputs 5 10 15 int main int itemsAr 3 int sum index itemsAr 0 1 2 index sum sum 0 for int index 0 index 5 index cout Enter the gpa for student index 1 cin gpasAr index output the contents of the array cout n nStudent Grade Point Averages n for index 0 index 3 index for int ind 0 ind 5 ind cout nGPA for student ind 1 gpasAr ind return 0 for index 2 index 1 index Topic 4 ch 8 Arrays This is okay You can also initialize all the elements to 0 using this method int itemsAr 3 itemsAr 0 2 itemsAr 1 12 itemsAr 2 1 This is not recommended or equivalently in the code This loop outputs the array 8 Initializing Arrays 2 int itemsAr 3 2 12 1 This loop initializes the array score 5 will not produce a compile time error It will produce a run time error if you have more elements than values in the list then the extras at the end default to 0 Arrays can be initialized at declaration as well all other values are Topic 4 ch 8 Arrays Initializing Arrays Simple variables can be initialized at declaration int price 0 0 is initial value of after declaration or equivalently in the code in bounds out of bounds First element always has an index of 0 7 0 1 2 3 4 are cout Enter an integer cin itemsAr index sum sum itemsAr index Output cout The sum of the numbers sum endl cout The numbers in reverse are cout itemsAr index return 0 11 What if we want to have 10 items What changes will we have to make 12 2 Defining a Constant as Array Size int main const int AR SIZE 10 int itemsAr AR SIZE int sum index sum 0 Always use defined named constant for array size Example const int AR SIZE 5 int scoresAr AR SIZE Note that it must be declared as an integer Improves readability Improves versatility Improves maintainability The number of elements must be known at compile time cout The sum of the numbers sum endl cout The numbers in reverse order are for index AR SIZE 1 index 1 index cout itemsAr index Topic 4 ch 8 Arrays Initializing using while loops Need to check if we are not at the end of our input file while inFile will handle this We need to check 2 things then int itemsAr AR SIZE inFile will return False if it is at the end of file int index int intInput index 0 load the array from keyboard input cout Enter the item enter 1 when done cin intInput while intInput 1 index AR SIZE itemsAr index intInput Initialize Both LCVs int index load the array from the keyboard What is wrong with this index 0 code while inFile index AR SIZE cout Enter the gpa for student index 1 cin itemsAr index index Change Both LCVs What if we want to read in from a file 15 Initializing from a File While we are not at the end of the file AND while we are still within bounds of our array cout Enter the item enter 1 when done cin intInput index 14 Initializing from a File Need to check for out of bounds as well as user controlled LCV Topic 4 ch 8 Arrays Note that this is AR SIZE 1 return 0 Using a constant is considered a best practice Need to make sure we don t Go out of bounds cout Enter an integer cin itemsAr index sum sum itemsAr index Topic 4 ch 8 Arrays for index 0 index AR SIZE index Works well if they have to enter 10 items NOTE Can t do this with a variable Instead of all those changes we can use a constant and just …