Lecture 13, CS 302-7 and 8, February 20

1. Review
1. Nested loops

i. How deep can you go? Unlimited

2. Simulation
1. Arrays
1. Store multiple values
2. Remember the parking lot metaphor?

i. This is the lot itself

3. Arrays have:

i. Type - eg double, int

ii. Length – eg [10]

4. Vocab

i. Element – item in a slot in the array, such as the car in a parking spot

ii. Index – [location]

1. the unique identifier for each spot in the array

5. Declare/Initialize

i. int[] numbers=new int[10];

1. Note – initializes each value to 0

ii. int[] numbers;

numbers=new int[10];

iii. int[] numbers = {1,2,3,4,5,6,7,8,9,10};

1. Note – don’t need to ‘new’ it. Size is based on # of numbers in init

iv. Note – must do one of these before trying to access array elements. Otherwise error.

6. Behind the scenes

i. Arrays are references [pointers]

1. Kind of like how strings were pointers, ints etc weren’t [primitives]

3. How to use arrays
1. Accessing

i. int[] numbers={1,2,3,4};

ii. Get ‘2’ by doing numbers[1].

1. “numbers sub 1”

iii. Note – indexes must be integers. numbers[1.5] doesn’t make sense

1. Can still use literals, variables, constants, calculations, method calls (rand.nextInt(10)), etc (note – not every way)

iv. Array length

1. Similar to strings

2. Arrays run from index 0 to index (length-1)

v. Calculating array length:

1. numbers.length

2. Note – no () after length

3. This is different than string length, which is .length()

vi. int[x] is just an int – you can use it like any other int.

1. Printing, arithmetic, etc

2. Things to remember about arrays

i. Fixed length

1. Cannot be changed after you have initialized it

2. Can change after declaring, though.

Eg int[] numbers; //do stuff; numbers=new int[var];

ii. Error if try to access element outside of range

1. run-time, not compile time, so be careful!

2. So, if we do int[] numbers=new int[10];

If we try to get int[10], java crashes

iii. Note – the exception will tell us why/where it failed, which is good

iv. Can re-initialize using new, but not using {} shortcut

3. Looping on an array – visiting all indexes.

i. Lends itself nicely to for loops

ii. For(int i=0;i<array.length;i++)

1. remember that arrays run from 0 to length-1, so above makes sense

4. Partially filled arrays – keep track of how many slots you’ve filled already, keep filling until full

i. Example – PartArray.java

1. Use of sentinel – abort early

4. HW - Read 6.3-6.4