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Functions

We have used functions already, this tutorial will show how to make them in order to seperate your code into more manageable sections. A function runs a block of code and usually returns an answer. (though in Java it can return void/nothing known as a sub)

We use the function println (System.out.println) to run code and print text to the console, or stdin.readLine() to get a line of text from the keyboard, or a better example String.toLowerCase() to remove capitols from text!
Format:

Code:
/* when writing your own functions do not put them inside other functions!, on other words create it outside of the
public static void main(){

}
// heres good...
*/
[variable type] [function name] ([parameter type 1][parameter 1],[parameter type 2][parameter 2],etc){

/* code to be run here */
return [variable type][answer]; //<-- gives the answer back

}

[variable type] = what format the function will return: void (nothing), int, long, double, bool etc...
[function name] = an informative name given to the function, names have same rules as variables
[parameter type][parameter] = you can send information to the function to work with, this is known as a parameter, in order to let the user send parameters you must declare them first inside the functions bracks (). You will see what I meen in the sample below.

Sample:

Code:
int answer=addNum(3,5); // call our new function!
System.out.println(""+answer); // display the answer...
// new declare the function
int addNum(int num1, int num2){

// note it takes 2 intergers (num1 and num2) (3 and 5)
return num1+num2;
// it returns (gives back) an integer (3+5) = 8

}

This small sample function 'addNum' adds to integers together and gives the answer...

---

Excersizes:

A few short tests to allow you to get the hand of functions :-)
Task 1
Using the code from 'addNum' create a new function named 'mulNum' which takes two integers a multiplies them together, (you may use '*' instead of plus) giving the answer... because multiplying creates significantly larger numbers, convert the function to return a long instead of int (see [variable type] above)

[click for answer]

Code:
System.out.println(""+mulNum(5,2));

long mulNum(int num1, int num2){

return num1*num2;

}

Task 2
Using the code from 'addNum' add a new parameter num3 and make the function add up 3 numbers num1,num2,num3 and return the result... call this 'add3Nums'

[click for answer]

Code:
System.out.println(""+add3Num(1,2,3));

int add3Num(int num1, int num2, int num3){

return num1+num2+num3;

}

Task 3
Create a new function named 'logon' which takes 2 parameters (String forename, String surname) uses if(String.compareTo()==0) to check if it is your forename and surname and return bool, true if it is and false if it isn't, you may want to recap on: the 'if' statement regarding comparing strings.

[click for answer]

Code:
if(logon("martin","sykes")) System.out.println("Welcome!");

bool logon(String forename, String surname){

if(forename.compareTo("martin")==0 && surname.compareTo("sykes")==0)){

return true;

} else{

return false;

}

}

Copyright (c) 2008, Martin Sykes.
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