1. Subprograms
Functions

2. Objectives Learn about functions: What they are How to define them
How to use them

3. Two Kinds There are two types of subprograms we will make use of:
A Procedure (Previous lesson)
A Function (This lesson)
For each of these we will clearly show:
How to define,
Where to define
How to call it within our programs

4. Function
A function is a mini-program within a program that performs a single task AND returns a result to the programmer, E.g. sqrt, pow
How to define a Function
General Syntax: (Yellow are customizable, Blue differentiate functions and procedures)
private static returnType Identifier(type1 identifier1, type2 identifier2, …) {
//code that is executed fully, whenever the //Subprogram is called
return value that matches the same type as returnType }
Example:
private static double CalcFloorArea(double length, double width) {
double area; area = length * width; return area; }

5. Breakdown
Needed if you plan to use the subprogram inside of main
Tells the Java compiler this is a function that will return a double to the programmer
private static double CalcFloorArea(double length, double width) {
double area; area = length * width; return area; }
The code to be executed EACH
time CalcFloorArea is called
The name of our subprogram. Naming follows the same rules as variables
except we use MixedCase to differentiate between variables and subprograms
quickly. This means EACH word starts with a capital
This is were parameters are defined, just like regular variables
REMEMBER: Not all subprograms will need them, but the ( , )
are ALWAYS necessary
Notice area is a local variable defined inside CalcFloorArea. It is not a parameter because it is NOT needed data
For the task, it is what is being calculated. area, like length and width will be deleted when the function completes

6. Time to Stamp
Using a function is the same as a procedure, except for one major difference.
It is our job as programmers to store the result of the function in a variable matching the return type of the function
Therefore we must use a variable
The next two slides will demonstrate this:
The first slide will use literal data
The second slide will ask the user for data and pass that data into the subprogram

7. Example: Literal values
public class MyProgram { public static void main(String[] args) { double floorArea = 0; floorArea = CalcFloorArea(2.5,2); System.out.println(“Floor Area: “ + floorArea); } private static double CalcFloorArea(double length, double width) { double area; area = length * width; return area; } }

8. Example: User values
import java.util.Scanner; public class MyProgram { static Scanner input = new Scanner(System.in); public static void main(String[] args) {
double roomLength = 0; double roomWidth = 0; System.out.print (“Enter Length: “); roomLength = Double.parseDouble(input.nextLine()); System.out.print (“Enter Width: “); roomWidth = Double.parseDouble(input.nextLine()); double floorArea = 0; floorArea = CalcFloorArea(roomLength, roomWidth); System.out.println(“Floor Area: “ + floorArea); }
private static double CalcFloorArea(double length, double width) { double area; area = length * width; return area; } }