Lecture 19, CS 302-6, October 17

1. Reminders
1. Exam 1 – October 20

i. no 2d arrays on exam

2. Program 2 – October 28
3. Office hours this week

i. Monday afternoon (not 3-4)

ii. Tuesday 12:30-2:30

iii. Wednesday afternoon

iv. Thursday 12:30-2:30, (exam 5-7)

v. Review session – Tuesday, 5-7, CS 1257

2. Review
1. Call stack tracing
2. Arrays as parameters and return values
3. 2d arrays
3. 2d+ arrays
1. Definition – ‘Array of arrays’
2. declaring

i. [][] or {{,},{,},…}

3. referencing element

i. [I][j]

ii. [row][column]

4. Example – TicTacToe.java
5. How to use

i. traversing – with nested for loops

1. Note – x[j] refers to an array itself if x is a 2 dimensional array

2. So, we have x.length, x[I].length

a. X.length is the number of rows in the entire array, x[I].length is the number of columns in the array stored at row i

3. Note – 2d arrays can contain different numbers of rows and columns.

ii. Example – TopicsChooser.java

4. Review
1. Order:

i. Arrays

ii. Methods

iii. Stepwise Refinement, Call Stack Tracing

iv. Scanner, random, etc

v. Loops

vi. Boolean Operators

vii. Conditional Statements

viii. Data Types

2. Array primer

i. Why arrays? They allow us to hold multiple pieces of data in one variable

ii. What is an array? List of elements

1. Each element can be referred to by an index

a. Start counting at 0

2. Size – number of elements

a. .length

iii. Declaring

1. type[] name=new type[length]

a. if we do this, we initialize each value to something

i. example – int[] initializes each value to 0

2. type[] name={x₁, x₂,…,x_i-1}, i is length

3. Can be of any type: int, double, String, etc

iv. Using

1. name[index]

v. Arrays as reference

1. keep in mind – variables only store one value

a. so, the variable for an array just stores a pointer to a memory location that stores the array

3. Example 1 – ArrayParameters.java (from spring 2011 exam)
4. HW – Prepare questions for Wednesday