The need for loops

NaughtySpirit Academy

Run example

static void main (String[] arguments) {
    print("Car #1");
    print("Car #2");
    print("Car #3");
} 

(get it?)

How loops help?

NaughtySpirit Academy

• Execute similar code multiple times
• Less code duplication
• Iterate over collections

While loop

NaughtySpirit Academy

Counting with care

while(CONDITION) {
    STATEMENTS;
}

For loop

NaughtySpirit Academy

for(INITIALIZATION; CONDITION; UPDATE;) {
    STATEMENTS;
}

When you know the number of loops

How to stop early?

NaughtySpirit Academy

Run example

public static void main (String[] args) {
    for(int i = 1; i <= 200; i++) {
	if(i == 10) {
	    break;
	}
	print("Car #" + i);
    }
}

break terminates the loop

How to skip one iteration?

NaughtySpirit Academy

Run example

public static void main (String[] args) {
    for(int i = 1; i <= 200; i++) {
	if(i == 10) {
	    continue;
	}
	print("Car #" + i);
    }
}

continue skips an iteration

Questions?

NaughtySpirit Academy

Why arrays?

NaughtySpirit Academy

Run example

public static void main (String[] args) {
    String car1 = "Nissan Micra";
    String car2 = "Peugeot 206";
    String car3 = "Smart for two";
    print(car1);
    print(car2);
    print(car3);
}

Array?

• Indexed list of values
• Can be of any type - int, String, double etc...
• All elements must be of the same type

NaughtySpirit Academy

Common gotchas

NaughtySpirit Academy

• First index: zero
• Last index: length - 1

How to create one?

NaughtySpirit Academy

To create array of given size use the operator new

public static void main (String[] args) {
    String[] cars = new String[5];
    print(cars);
}

Run example

Array initialization

NaughtySpirit Academy

Curly braces can be used to initialize an array.
ONLY when you declare the variable!

public static void main (String[] args) {
    String[] cars = {"Nissan Micra", "Peugeot 206"};
    print(cars);
}

Run example

Accessing arrays

NaughtySpirit Academy

Access an element from array using the [ ] operator

public static void main (String[] args) {
    String[] cars = {"Nissan Micra", "Peugeot 206"};
    print(cars[0]);
}

Run example

Does the size matter?

NaughtySpirit Academy

Each array has a built-in length variable that contains the size of the array

public static void main (String[] args) {
    String[] cars = {"Nissan Micra", "Peugeot 206"};
    print(cars.length);
}

Run example

2D Array or Matrix

NaughtySpirit Academy

Grid of rows and columns 

2D Array or Matrix (2)

NaughtySpirit Academy

public static void main (String[] args) {
    String[][] cars = {
        {"Micra", "350Z", "Primera"}, 
        {"206", "306", "406"}};
    print(cars);
 
    // Alternative
    String[][] cars1 = new String[2][3];
    cars1[0][0] = "Micra";
}

Run example

Initialize

Looping through an array

NaughtySpirit Academy

Or how to combine arrays and loops

public static void main (String[] args) {
    String[] cars = {"Nissan Micra", "Peugeot 206"};
    for(int i = 0; i < cars.length; i++) {
	print(cars[i]);
    }
}

Run example

Math Wars is back

Questions?

NaughtySpirit Academy