What can we do with iterations

1
What can we do with iterations?
Life is just one damn thing after another
Mark Twain
2
Comparisons

• lt, gt, lt and gt can only be used with numbers and
  characters
• Is true greater than false?

public class JackandJill public static
void main(String args) String s1
"Jack went up the hill." String s2
"Jack went up the hill." if (s1 s2)
System.out.println( "The strings are
the same.")
3
Comparison
else if (s1 ! s2)
System.out.println( "The strings are
different.")

The output is The strings are different.
4
Comparison

• A Correct Test for String Equality

public class JackandJill public static
void main(String args) String s1
"Jack went up the hill." String s2
"Jack went up the hill." if
(s1.equals(s2)) System.out.println(
"The strings are the same.")
else System.out.println( They the
different.")
5
How Much Does the King Owe

• For every square on the chessboard, Ill double
  the wheat debt

public class CountWheat public static void
main(String args) int current,
totalAmount final int NUM_OF_SQUARES
64 current 1 totalAmount
0 for (int i1 i lt NUM_OF_SQUARES
i) current 2
totalAmount current
System.out.print(totalAmount \t )

6
How Much Does the King Owe
if (i 4 0)
System.out.println()
What Happened???
The output is

• 6 14
  30
• 126 254
  510
• 2046 4094
  8190
• 32766 65534
  131070
• 262142 524286
  1048574 2097150
• 4194302 8388606
  16777214 33554430
• 67108862 134217726 268435454
  536870910
• 1073741822 2147483646 -2
  -2
• -2 -2
  -2 -2
• -2 -2
  -2 -2

7
How Much Does the King Owe

• Testing for overflow

public class CountWheat public static void
main(String args) int current,
totalAmount final int NUM_OF_SQUARES
64 current 1 totalAmount
0 for (int i1 i lt NUM_OF_SQUARES
i) current 2
totalAmount current if (current
lt 0) System.out.println("Error
Overflow") break
8
How Much Does the King Owe
System.out.print(totalAmount \t ) if (i
4 0) System.out.println()

The output is

• 6 14
  30
• 126 254
  510
• 2046 4094
  8190
• 32766 65534
  131070
• 262142 524286
  1048574 2097150
• 4194302 8388606
  16777214 33554430
• 67108862 134217726 268435454
  536870910
• 1073741822 2147483646 Error Overflow

9
Unstoppable for loop
for (long iLong.MAX_VALUE 2 ilt
Long.MAX_VALUE i) / .../

• How many times will that for loop execute? Until
  you kill the process!

• It will loop endlessly because I can never get
  bigger than Long.MAX_VALUE to terminate the loop.

10
Walls, walls everywhere

• How can you make your way out of a maze ?

Exit

• Simple! Walk along the walls.

11
Walls, walls everywhere
public class MazeSolver public static void
main(String args) while (notAtExit)
if (!wallToRight) turnRight()
moveForward()
else if (!wallAhead) moveForward()
else
turnLeft()
12
Walls, walls everywhere

• What does the solution look like?

13
Palindrome Checkup

• Palindromes can be read from either direction
• For example Racecar

public class PalindromeTester
//------------------------------------------------
----------------- // Tests strings to see if
they are palindromes. //----------------------
-------------------------------------------
public static void main (String args)
String str, another "y" int left,
right while (another.equalsIgnoreCase("y"
)) // allows y or Y
System.out.println ("Enter a potential
palindrome") str readString()
14
Palindrome Checkup
left 0 right str.length() -
1 while (str.charAt(left)
str.charAt(right) left lt right)
left right--
System.out.println() if (left lt right)
System.out.println ("That string is
NOT a palindrome.") else
System.out.println ("That string IS a
palindrome.") System.out.println()
System.out.print ("Test another palindrome
(y/n)? ") another readString()

15
An Alarm Clock

• Develop an alarm clock and set its timer

public class AlarmClock public static
void main (String args) int hour,
minute, second, alarmHour, alarmMinute,
alarmSec // set the current time
do System.out.print(Enter the hour
) hour readInt() while
((hour gt HOURS_PER_DAY - 1) (hour lt 0))
do System.out.print(Enter the
minutes ) minute readInt()
while ((minute gt MINUTES_PER_HOUR - 1)
(minute lt 0))
16
An Alarm Clock
do System.out.print(Enter the
seconds ) seconds readInt()
while ((seconds gt SECONDS_PER_MINUTE - 1)
(seconds lt 0)) // set the alarm do
System.out.print(Enter the alarm
hour ) aralmHour readInt()
while ((aralmHour gt HOURS_PER_DAY-1)
(aralmHour lt 0)) do
System.out.print(Enter the alarm minutes )
alarmMinute readInt() while
((minute gt MINUTES_PER_HOURS-1) (alarmMinute lt
0))
17
An Alarm Clock
do System.out.print(Enter the
alarm seconds ) alarmSeconds
readInt() while ((alarmSeconds gt
SECONDS_PER_MINUTE-1)
(alarmSeconds lt 0)) // run the
clock while ((hour ! alarmHour)
(minute ! alarmMinute)
(second ! alarmSeconds)) for (int
time0 time lt SECOND time)
seconds if (seconds
SECONDS_PER_MINUTE) seconds
0 minute
18
An Alarm Clock
if (minute MINUTES_PER_HOUR)
minute 0 hour
if (hour HOURS_PER_DAY)
hour 0
// alarm goes off System.out.println(
Wake up!!! Wake up!!!)
19
Drawing using loops

• Using for loops to draw shapes on the screen

public class Drawer public static
void main (String args) for (int i0
i lt 5 i) for (int j0 j lt I1
j) System.out.print()
System.out.println()

The output is

20
Factorial calculation

• Given a number, calculate its factorial
• N! N(N-1)(N-2).21

public class Factorial public static
void main (String args) long result
1 int number do
System.out.print(enter a number )
number readInt() while (number lt 0)
for (int inumber i gt 0 i--)
result i System.out.println(result
is result)
21
Fibonacci series Golden Ratio

• Each term is the sum of the two previous ones
• 0 1 1 2 3 5 8 13 21 34 55.

public class Fibonacci public static
void main (String args) long lower
0 long higher 1 int
iterations readInt() for (int i1 i
lt iterations i)
System.out.print(higher \t )
long temp higher higher lower
lower temp if (i 10
0) System.out.println()

22
Fibonacci series Golden Ratio

• The Golden Ratio is the ratio of the last two
  terms in this infinite series.
• It is supposed to be the ideal proportion in
  architecture and art, and was used in the design
  of ancient Greek temples.
• If the number of iterations is 45, the last two
  terms are 701,408,733 and 1,134,903,170 and
  their ratio is 0.618034 Close enough for
  government work.

23
Calculator

• Create the equivalent of a four-function
  calculator.

public class Calculator public static
void main (String args) int operand1,
operand2 char operator
while(true) System.out.print(Enter
the first operand ) operand1
readInt() do
System.out.print(Enter the operator
(, -, , /)) operator
readChar() if ((operator
) (operator -) (operator )
(operator /))
break while
(true)
24
Calculator
System.out.print(Enter the second
number ) operator2 readInt()
switch (operator)
case
System.out.println(operator1 operator2

(operator1 operator2))
break case -
System.out.println(operator1 - operator2

(operator1 - operator2))
break case
System.out.println(operator1 operator2

(operator1 operator2))
break
25
Calculator
case /
System.out.println(operator1 / operator2

(operator1 / operator2))
break
System.out.print(Another calculation ?)
char answer readChar() if
(answer y) (answer Y)
continue else // anything buy y or
Y means no break

26
Bank Investment

• What will my balance be in X years?

public class Investment public static
void main (String args) double
amount double rate int years
do
System.out.print(Enter initial amount )
amount readDouble() while
(amount lt 0.0) do
System.out.print(Enter annual rate )
rate readDouble() while (rate lt
0.0)
27
Bank Investment
do System.out.print(Enter
number years ) years
readInt() while (year lt 0)
for (int I0 I lt year I) amount
(1.0 rate) System.out.println(After
years years, you will have amount
)
28
Y2K
switch (month) case 4 case 6 case 9 case
11 numOfDays 30 break case
2 switch (year 4) case
0 switch (year 400)
case 100 case 200 case 300
numOfDays 28
break default
numOfDays 29
break default
numOfDays 28 break
default numOfDays 31