Algorithms

If you plan on continuing with programming after grade 11, you will probably want to make a document where you can write down useful and clever algorithms.

making a counter You'll need to do this at various places to count things

int counter = 0;
counter++;

keeping a total This is just the basic part. You'll have to put it in the correct place

int total = 0;
total += number;

Exchanging two variables here they are two ints called a and b

Sometimes one needs to do this, especially when sorting data. You can't just say a=b and b=a because both variables end up being the same number (b). You have to make a temporary variable to store one of the numbers so that it doesn't get overwritten.

int temp = a;
a = b
b = temp;

Error Checking

• All type input needs to be checked to make sure that it is the correct type.
• You need to make sure that a number is non-zero if you're dividing (so you don't divide by zero)
• Sometimes there is a range of numbers that are the only numbers allowed.

Checking range of inputThis assumes that we're using Scanner for input, but it works with other methods too.

//check to see if it's between 1 and 10
int num = sc.nextInt();
while (num < 1 || num > 10) {
   System.out.println("num must be from 1 to 10");
   num = sc.nextInt();
}

Getting a certain data type. This will prevent the Scanner from crashing the program if someone types in a word instead of a number

This is complicated enough, that it's probably worth making a whole class for things like this.
Call it Utility class (or something similar, but not "util") and add useful things to it.

/* Usage: 
In your main program, you can type:   int x = Utility.getInt();
or add a message to be printed:  int x = Utility.getInt("Enter your mark");
and  double speed = Utility.getDouble();
*/
import java.util.Scanner;
public class Utility {

	static int getInt() { return getInt(""); }

	static int getInt(String s) {
 		Scanner sc = new Scanner(System.in);
 		if (s.length() == 0) s = "Please enter an integer: ";
 		System.out.print(s);
 		while(! sc.hasNextInt()){
 			System.out.println("Integer required");
 			System.out.print(s);
 			sc.nextLine(); //cleans up crap
 		}
 		return sc.nextInt();
 	}

  	static double getDouble() { return getDouble(""); }

 	static double getDouble(String s) {
 		Scanner sc = new Scanner(System.in);
 		if (s.length() == 0) s = "Please enter a double: ";
 		System.out.print(s);
 		while(! sc.hasNextDouble()){
 			System.out.println("Double required");
 			System.out.print(s);
 			sc.nextLine(); //cleans up crap
 		}
 		return sc.nextDouble();
 	} 
}