If all the code snippets below assume properly that an ...



IMPORTANT CONCEPTS TO UNDERSTAND in JAVA:

(answer key)

If all the code snippets below assume properly that an array, myArray, has been properly instantiated then;

How to average correctly

int x, y, sum;

double average;

sum = x + y;

average = (double) sum / 2;

// the key here is to cast the sum to a double.

How to average correctly in an array

int x, y, sum;

double average;

for (int i = 0; i < myArray.length; i++)

   sum +- myArray[i];

average = (double) sum / myArray.length;

// the key here is to cast the sum to a double to not lose decimal data

How to find max/min in an array

int max, min;

max = myArray[0] ;

min = myArray[0];

for (int i = 0; i < myArray.length; i++)

{

if (myArray[i] > max)

   max = myArray[i];

if (myArray[i] < min)

   min = myArray[i];

}

// the key here is to properly initialize max and min before entering the for loop

How to swap elements

int x, y, temp;

temp = x;

x = y;

y = temp;

// the key here is to perform the swap in the correct order

How to swap elements in an array

int x, y, temp;

temp = myArray[thisIndex];

myArray[thisIndex] = myArray[thatIndex];

myArray[thatIndex] = temp ;

// the key here is to perform the swap in the correct order

How to reverse an array

int x, y, temp;

for (int i = 0; i < myArray.length / 2; i++)

{

temp = myArray[i];

myArray[i] = myArray[myArray.length – 1 - i];

myArray[myArray.length – 1 - i] = temp ;

}

// the key here is to perform the swap in the correct order through just half of the array

How to increase the size of an array

int count;

if (count = = myArray.length)

{

myArrayType[] temp = new myArrayType[myArray.length * 2];

for (int i = 0; i < myArray.length; i++)

temp[i] = myArray[i];

myArray = temp;

}

Explain the selection sort/insertion sort algorithms

This is outlined very well in your text book!

How to tell if a number is odd or even

int x;

boolean isEven = false;

if (x % 2 = = 0)

   isEven = true;

// otherwise isEven returns false

How to turn a number into a String

int x;

String y;

X = 125;

y = “ “ + 125; // do not attempt to cast the number into a String!!!

How to prompt users for input. What lines are necessary to “scan” for input?

// First, you must make the scanner class available…

import java.util.Scanner;

public class MyJavaProgram

{

// Then you must initialize the scanner object

Scanner scan = new Scanner(System.in);

String message;

// Finally, you must prompt for input

System.out.println(“Please enter info: “);

message = scan.next(); // use scan.next() and scan.nextline() for Strings,

// use scan.nextInt(); for integers!

How to compute/generate a random number.

// HINT: you will need to use the math class to do this.

int num1;

double num2;

// First, generate random integer from 0 to 9

num1 = (int)(Math.random() * 10);

System.out.println ("From 0 to 9: " + num1);

// Second, generate random integer from 1 to 10

num1 = (int)(Math.random() * 10 + 1);

System.out.println ("From 1 to 10: " + num1);

// Third, generate random integer from 20 to 34

num1 = (int)(Math.random() * 15 + 20);

System.out.println ("From 20 to 34: " + num1);

// Fourth, generate random decimal from 0 to 0.99

num2 = Math.random();

System.out.println ("A random double [between 0-1]: " + num2);

// Fifth, generate random decimal from 0 to 5.99

num2 = Math.random() * 6;

System.out.println ("A random double [between 0-6]: " + num2);

How to extract individual digits from an integer.

// HINT: the concept is called modulus and you will need to use % operator(remainder)

int num = 12345;

int digitNum; // will be the extracted number

// get the ones digit

digitNum = num % 10; // returns 5

// get the tens digit

// to get the to the tens digit, we first divide by 10 (12345/10=1234)

num /= 10;

// now we can compute the remainder

digitNum = num % 10; // returns 4

// get the hundreds digit

// to get the to the hundreds digit, we first divide by 100 (12345/100=123)

num /= 100;

// now we can compute the remainder

digitNum = num % 10; // returns 3

// etc.

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