highschool/Grade 10/Computer Science/ICS4U1/Class_1.md

Class 1 Notes

Array Review

What is an Array:

• An (reference) object used to store a list of values
• A contiguous block of memory is used to store the values.
• Each cell holds a value
• All the values are the same type
• It can store all kinds of data, int, double, object, etc, the type stored can be primitive (int) or reference (object)
• Once an array has been created, the number of cells cannot be changed.

Example

index	0	1	2	3	4	5	6	7
value	80	120	103	138	94	109	83	117

• The array name is bowlingScores, you can access specific value at a specific index: eg. bowlingScores[3] = 138.
• If there are \(`n`\) cells in the array the indexes will be from \(`0`\) to \(`n-1`\), arrays are 0-index based.
• If we are acessing a value out of the range of the array, such as bowlingScores[8], then we get an ArrayOutOfBounds Error.

Initializing Arrays

• General syntax to declare an array:

final int MAX = 8;
int [] bowlingScores= new int[MAX];
bowlingScores[0] = 180; // initializing
bowlingScores[1] = 120; // initializing
...

• To intialize all the values at once, we can do:

int[] luckyNumbers = {2, 3, 10, 4, 17, 21}; // known values

Summing Values In An Array

In Main

int sum; // declare an accumulator
sum = 0;
for(int i=0; i<MAX i++) {
    sum = sum + list[i]; // sum += list[i];
}
System.out.println("The sum of all values in the array in the array is " + sum);

As A Method

public int findSum(int [] list) {
    int sum; // declare an accumulator
    sum = 0;
    for(int i=0; i<MAX i++) {
        sum = sum + list[i]; // sum += list[i];
    }
    System.out.println("The sum of all values in the array in the array is " + sum);
}

Method That Returns An Array

public int[] getNewList() {
    int [] list = new int[10];
    for(int i=0; i<10; i++) {
        list[i] = i;
    }
    return list;
}