Java

TOPIC 19 – WHILE LOOPS – Part 1

LESSON WORK

QUESTION 1

How many iterations will there be for each of the following programs? In other words, how many times will the following programs say “Hi” to you?

a)

int a = 5;

while (a <= 9)

{

System.out.println("Hi");
a++;

}

b)

int a = 12;

while (a != 9)

{

System.out.println("Hi");
a--;

}

c)

int x = 0;

while (x <= 10)

{
x++;

System.out.println("Hi");
x++;

}

d)

int a = 0;

while (a == 4)

{

System.out.println("Hi");
a++;

}

e)

int c = 5;

while (c != 6)

{

System.out.println("Hi");
c=c+2;

}

QUESTION 2 – SEQUENCES

Write the program that will use while loops to output each of the sequences seen below with all numbers separated by a comma. You should use one while loop per sequence.

a) 1,2,3,4,5,6,7,8,9,10,

b) 10,20,30,40,50,60,70,80,90,100

c) 20,19,18,17,16,15,14,13,12,11,10

d) 1,4,9,16,25,36,49,64,81,100

e) 1,2,4,8,16,32,64,128,256,512,1024

QUESTION 3 – USER DECIDES

Write a program that asks the user for a low number and a high number. It will then output all numbers between the two provided numbers.

Sample output:

Enter a number:

10

Enter another number:

14

Your numbers are:

10

11

12

13

14

Extra: Can you also make the program deal with the situation of the two numbers being entered in the wrong order? So the user would enter the larger number first and then smaller number next.

QUESTION 4 – COLLATZ SEQUENCE

Background

In the 1930s, a mathematician named Lothar Collatz looked at a special sequence of numbers. In the sequence, when a number is even, then the next number will be half of that number. When a number is odd, then the next number will be 3 times than number plus 1. Here is an example for the sequence that starts with 10.

10,5,16,8,4,2,1,4,2,1,4,2,1,…

Because of the cycle that begins when we hit 1, we usually stop the sequence at 1. So the Collatz sequence starting with 10 is:

10,5,16,8,2,1,

Collatz made an interesting observation. No matter what number we start with, we seem to always get to 1. However, despite many many efforts, nobody has ever proven this to be true. So it is possible that we find a number that will not lead to the value 1.

Work

Write the program that asks the user for a positive integer that will the starting point for the Collatz sequence. Use a while loop that will output the entire sequence ending at 1.

Hint

You need to loop until the value of the sequence is equal to 1. So that should be your condition.