arrays

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arrays

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If a variable is like a 'mailbox', an array is like the mailboxes at a post ... if(Mystery('antelope', 'e')) cout 'One' endl; else. cout 'Two' endl; ... – PowerPoint PPT presentation

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Title: arrays

1
arrays

An array is a collection of data, all of the same
data type, that is accessed with an index
If a variable is like a "mailbox", an array is
like the mailboxes at a post office or an
apartment building a row of otherwise identical
boxes with different numbers.
We tell C we want to make an array by using
(square brackets)

2
arrays

int naNums3
naNums0 5
naNums1 -4
naNums2 17

naNums
garbage
garbage
garbage
0 1 2
5
-4
17
naNums
0 1 2
3
arrays

May be declared and initialized in one line
int naNums 5,-4,17
Are "zero-based" First index is 0
coutltltnaNums1 //displays -4
You can make an array of any data type
char caLetters a, b, c
string saAnswers yes, no
Good Style The first letter should show data
type, followed by a for array

4
A Simple Program using an array

include ltiostream.hgt
include ltstdlib.hgt
int main()
double daNums 5, 1.5, 7, 3.2
for(int nIndex 3 nIndex gt 0 nIndex--)
coutltltdaNumsnIndexltlt", "
system("PAUSE")
return 0

5
Don't confuse the index with the value that is
stored there

double daNums 5, 1.5, 7, 3.2
daNums2
2 is the index (think apartment number)
7 is the value that is stored at index 2

6
Practice Quiz Question What is the output of
this program?

include ltiostream.hgt
include ltstdlib.hgt
include ltstringgt
using namespace std
int main()
string saWords "The", "Quick", "Brown",
"Fox",
"Jumped", "Over", "The", "Lazy", "Red",
"Dog"
for(int nIndex 0 nIndex lt 10
nIndexnIndex2)
coutltltnIndexltlt" "ltltsaWordsnIndexltltendl
system("PAUSE")
return 0

7
Practice Quiz Questions

For the following function
void TripleIt(int nNum)
coutltlt3nNumltltendl
(T/F) TripleIt(int nNum) is a correct function
call
(T/F) void TripleIt(int nNum) is a correct
function call
(T/F) TripleIt(3) is a correct function call
(T/F) int nI3 TripleIt(nI) is a correct
function call
(T/F) void TripleIt(int nNum) is a correct
function prototype
(T/F) void TripleIt(int nNum) is a correct
function header
What is the output of the following program?
void Mystery(int nNum1, int nNum2)
int main()
int nA 5, nB 6
Mystery(nA,nB)
coutltltnAltlt", "ltltnBltltendl

8
Practice Quiz Question What is the output of
this program?

include ltiostream.hgt
include ltstdlib.hgt
const int nNUM_MAILBOXES 5
int main()
int naNumsnNUM_MAILBOXES
for (int nIndex 0 nIndex lt nNUM_MAILBOXES
nIndex)
if(nIndex 2 0) //if nIndex is even
naNumsnIndex nIndex
else if (nIndex 3 0) //if nIndex is a
multiple of 3
naNumsnIndex 17
else
naNumsnIndex 3
for(int nIndex 0 nIndex lt nNUM_MAILBOXES
nIndex)
coutltltnaNumsnIndexltlt", "
system("PAUSE")
return 0

9
strings and outtextxy

outtextxy was written before the new style C
strings, so it expects an "old-fashioned" C
string
There is a conversion function .c_str() converts
an C string to an "old-fashioned" C string.
string sString "Hello World!"
outtextxy(30,240,sString.c_str())

10
A string is an array

You can use with a string, just like with an
array
string sWord "Hello World"
coutltltsWord0ltltendl
//displays 'H'

11
A string is an array

You can use with a string, just like with an
array
string sWord "Hello World"
coutltltsWord0ltltendl
//displays 'H'
coutltltsWord.length()ltltendl
//displays 11

12
A string is an array

You can use with a string, just like with an
array
string sWord "Hello World"
coutltltsWord0ltltendl
//displays 'H'
coutltltsWord.length()ltltendl
//displays 11
coutltltsWordsWord.length()-1
ltltendl
//displays 'd'

13
bool

A data type, just like int, double, char
A bool mailbox can only hold one of two values
true or false
bool bState true
bState (nNum gt 3)
You can use a bool anywhere you would use a
condition
if(bState)
coutltltnNum is greater than 3

14
Problem Write a function that determines if a
student will graduate

bool IsGraduating(int nCredits,
bool bPassedExam)
if(nCredits gt 230 bPassedExam)
return true
else
return false

15
Problem Write a function that determines if a
student will graduate

Here's the same function in one line of code!
bool IsGraduating(int nCredits,
bool bPassedExam)
return(nCredits gt 230 bPassedExam)

16
What is the output of this program?
bool IsMatch(string sWord)
if(sWord.length()gt3) return sWord0
sWord2 else return false

include ltiostream.hgt
include ltstdlib.hgt
include ltstringgt
using namespace std
bool IsMatch(string sWord)
int main()
if(IsMatch("elephant"))
coutltlt"Match 1"ltltendl
if(IsMatch("alligator"))
coutltlt"Match 2"ltltendl
if(IsMatch("ox"))
coutltlt"Match 3"ltltendl
if(IsMatch("pup fish"))
coutltlt"Match 4"ltltendl
system("PAUSE")
return 0

17
getline()

string sName
coutltlt"Please enter your name "
getline(cin,sName)
//user enters Mr. Simon
coutltlt"You entered "ltltsNameltltendl
//displays You entered Mr. Simon
Stores the entire line, including spaces

18
getline()

Rule Don't use cin and getline in the same
program if you can avoid it.
If you really must use both cin and getline in
the same program, it is a good idea to use a
cin.ignore(80,\n) after each cin to flush the
input stream of any extra end of line
characters.

19
What is the output of this program?

bool Mystery (string sWord, char cLetter)
int main()
if(Mystery("antelope", 'e'))
coutltlt"One"ltltendl
else
coutltlt"Two"ltltendl
if(Mystery("aardvark", 'a'))
coutltlt"Three"ltltendl
else
coutltlt"Four"ltltendl
system("PAUSE")
return 0
bool Mystery(string sWord, char cLetter)
int nSum 0
for(int nI 0 nI lt sWord.length() nI)
if(sWordnI cLetter)

20
"Adding" strings

What would this code display?
string sWord
"Hello " "there"
coutltltsWordltltendl

21
"Adding" strings

What would this code display?
string sWord
"Hello " "there"
coutltltsWordltltendl
/Sample Output
Hello there/

22
"Adding" strings

What would this code display?
string sWord
"Hello " "there"
coutltltsWordltltendl
/Sample Output
Hello there/

23
"Adding" strings

When you use the operator with strings, it's
called "Concatenation"
That just means "adding on to the end"
string sWord
"Hello " "there"
coutltltsWordltltendl
/Sample Output
Hello there/

24
ctype.h

bool isalpha(char cChar)
returns true if cChar is a letter of the
alphabet, false otherwise
bool isalnum(char cChar)
returns true if cChar is a letter or number,
false otherwise
char tolower(char cChar)
returns the lowercase of cChar
char toupper(char cChar)
returns the uppercase of cChar

25
Problem Write a function that returns an upper
case version of a string

include ltiostream.hgt
include ltstdlib.hgt
include ltstringgt
using namespace std
string MakeUpper(string sWord)
int main()
string sWord "hello"
coutltltMakeUpper(sWord)ltltendl //HELLO
system("PAUSE")
return 0
string MakeUpper(string sWord)
???

26
Problem Write a function that returns an upper
case version of a string

int main()
string sWord "hello"
coutltltMakeUpper(sWord)ltltendl //HELLO
system("PAUSE")
return 0
string MakeUpper(string sWord)
string sNewWord
???
return sNewWord

27
Problem Write a function that returns an upper
case version of a string

int main()
string sWord "hello"
coutltltMakeUpper(sWord)ltltendl //HELLO
system("PAUSE")
return 0
string MakeUpper(string sWord)
string sNewWord ""
for(int nI 0 nI lt sWord.length() nI)
sNewWord (char)toupper(sWordnI)
return sNewWord

28
What is the output?

include ltiostream.hgt
include ltstdlib.hgt
include ltctype.hgt
include ltstringgt
using namespace std
string Mystery(string sText)
int main()
coutltltMystery("Testing, 1,2,3")ltltendl
system("PAUSE")
return 0
string Mystery(string sText)
string sNew ""
for(int nI 0 nI lt sText.length() nI)
if(!isalpha(sTextnI))
sNew sNew "x"
else if(tolower(sTextnI)sTextnI)

29
More string functions

Comparison
!
lt lt gt gt //same case alphabetically
Input cin
string sName
coutltlt"Please enter your name "
cingtgtsName
//user enters Mr. Simon
coutltlt"You entered "ltltsNameltltendl
//displays You entered Mr.
Input with cin is delimited by whitespace

30
More string functions

Concatenation (the operator)
string sString1 "Hello "
string sString2 "World!"
string sString3 sString1 sString2
coutltltsString3ltltendl //Hello World!
Substrings
coutltltsString1.substr(3,2)ltltendl // lo
Indexing
coutltltsString11ltltendl //e
Length
coutltltsString1.length()ltltendl //6
Find
coutltltsString1.find('l')ltltendl //2

31
What is the output of this program?

include ltiostream.hgt
include ltstdlib.hgt
include ltstringgt
using namespace std
int main()
string sOne "abccba"
string sTwo "xyzzyx"
string sThree sOne sTwo
coutltltsThreeltltendl
coutltltsThree.length()ltltendl
coutltltsThree11ltltendl
coutltltsThree.find('c')ltltendl
coutltltsThree.substr(4,3)ltltendl
system("PAUSE")
return 0

32
The Palindrome Algorithm

An Algorithm is the steps you take to solve a
problem
What steps would you take to see if the following
word is a palindrome?
rewriter

33
The Palindrome Algorithm

rewriter

34
The Palindrome Algorithm

rewriter

35
The Palindrome Algorithm

rewriter

36
The Palindrome Algorithm

Start by comparing the first and last letters
If they are the same, does that mean the word is
a palindrome?
If they are different, does that mean the word is
NOT a palindrome?
rewriter
01234567

37
The Palindrome Algorithm

Start by comparing the first and last letters
If they are the same, does that mean the word is
a palindrome?
If they are different, does that mean the word is
NOT a palindrome?
rewriter
01234567
int nFirst 0
int nLast sWord.length() 1
if(sWordnFirst!sWordnLast)
????

38
The Palindrome Algorithm

Start by comparing the first and last letters
If they are the same, does that mean the word is
a palindrome?
If they are different, does that mean the word is
NOT a palindrome?
rewriter
01234567
int nFirst 0
int nLast sWord.length() 1
if(sWordnFirst!sWordnLast)
return false

39
The Palindrome Algorithm

rewriter
01234567
int nFirst 0
int nLast sWord.length() 1
if(sWordnFirst!sWordnLast)
return false
else
???

40
The Palindrome Algorithm

rewriter
01234567
int nFirst 0
int nLast sWord.length() 1
while(???)
if(sWordnFirst!sWordnLast)
???
else
???
???

41
Getting data in and out of functions

Arguments allow data to passed into a function
There are two ways to data out of a function
Pass by reference arguments
return statements

42
An Add function with a return statement

include ltiostream.hgt
include ltstdlib.hgt
int Add(int nNum1, int nNum2)
int main()
coutltltAdd(2,2)ltltendl
system("PAUSE")
return 0
int Add(int nNum1, int nNum2)
return nNum1 nNum2

43
You could write an Add function with pass by
reference arguments, but it would be uglier

include ltiostream.hgt
include ltstdlib.hgt
void Add(int nNum1, int nNum2, int nAnswer)
int main()
int nSum
Add(2,2,nSum)
coutltltnSumltltendl
system("PAUSE")
return 0
void Add(int nNum1, int nNum2, int nAnswer)
nAnswer nNum1 nNum2

44
Good Style

Always use a return statement to get data out of
a function, unless
You need to get more than one piece of data out
of the function (then use pass by reference
arguments)
Avoid using both pass by reference and return
statements

45
Practice Quiz Question Find the output

int Mystery(int nNum)
int main()
coutltltMystery(2)ltltendl
coutltltMystery(3)ltltendl
coutltltMystery(Mystery(2))ltltendl
system("PAUSE")
return 0
int Mystery(int nNum)
int nSum 0
while(nNum gt 0)
nSum nSum nNum
nNum--
return nSum

46
Functions can be used for value or effect

An effect might be to display something on the
screen, make a noise, or stop the program
Functions that have an effect usually have void
as the return type
Here are some prototypes
void circle (int nX, int nY, int nRadius)
void line (int nX1, int nY1, int nX2, int nY2)
void delay (int nMillisec)
void cleardevice ()
void closegraph ()

47
Functions can be used for value or effect

A value could be an int, char, string, bool or
any other data type
Functions that return a value have a return type
other than void
bool kbhit ()
char getch ()
bool Palindrome (string sText)
bool isalpha(char cChar)
char tolower(char cChar)

48
A common mistake

Beginning programmers often forget to use the
value a function returns
coutltlt"Please enter a word"ltltendl
getline(cin,sWord)
Palindrome(sWord) //oops!

49
A common mistake

Palindrome is returning a true or false, but this
program isn't using it
coutltlt"Please enter a word"ltltendl
getline(cin,sWord)
Palindrome(sWord) //oops!
true

50
A common mistake

the returning true or false should be stored in
a variable or used in a condition
coutltlt"Please enter a word"ltltendl
getline(cin,sWord)
if(Palindrome(sWord)) //better!
coutltlt" is a palindrome"ltltendl

51
A common mistake

the returning true or false should be stored in
a variable or used in a condition
coutltlt"Please enter a word"ltltendl
getline(cin,sWord)
bool bAnswer Palindrome(sWord)
if(bAnswer) //this is also better!
coutltlt" is a palindrome"ltltendl

52
What is the output?

int main()
char caChars 'x', '1', '?', ' ', 'X',
''
for(int nI 0 nI lt 6 nI)
char cChar caCharsnI
coutltltcChar
if(isalpha(cChar))
if(toupper(cChar) cChar)
coutltlt"p"
if(tolower(cChar) cChar)
coutltlt"w"
if(isalnum(cChar))
coutltlt"t"
if(!isalnum(cChar))
coutltlt"o"
coutltltendl

53
2 dimensional arrays

Can be thought of as a grid with rows and
columns

column 0 1 2
-3
-1
5
row 0
7
12
13
row 1
54
2 dimensional arrays

int naNums23 -3, -1, 5,
7, 12, 13
//Note rows first, then columns
coutltltnaNums12 //displays 13
coutltltnaNums21 //Crash!

column 0 1 2
-3
-1
5
row 0
7
12
13
row 1
55
A 2 dimensional array of SAT words

string saSAT32
"accomplish", "To bring to pass.",
"adhere", "To stick fast or together.",
"amity", "Friendship."

column 0 1
accomplish
To bring to pass
row 0
adhere
To stick fast or together
row 1
amity
Friendship
row 2
56
A 2 dimensional array of SAT words

int nCorrect rand()??
coutltlt"Which word has the definition "
ltltsaSAT????ltltendl

column 0 1
accomplish
To bring to pass
row 0
adhere
To stick fast or together
row 1
amity
Friendship
row 2
57
A 2 dimensional array of SAT words

int nCorrect rand()3
coutltlt"Which word has the definition "
ltltsaSAT????ltltendl

column 0 1
accomplish
To bring to pass
row 0
adhere
To stick fast or together
row 1
amity
Friendship
row 2
58
A 2 dimensional array of SAT words

int nCorrect rand()3 //let's say 1
coutltlt"Which word has the definition "
ltltsaSATnCorrect1ltltendl

column 0 1
accomplish
To bring to pass
row 0
adhere
To stick fast or together
row 1
amity
Friendship
row 2
59
A 2 dimensional array of SAT words

int nCorrect rand()3 //let's say 1
coutltlt"Which word has the definition "
ltltsaSATnCorrect1ltltendl
//Let's make A the correct answer
coutltlt"A "ltltsaSAT????ltltendl

column 0 1
accomplish
To bring to pass
row 0
adhere
To stick fast or together
row 1
amity
Friendship
row 2
60
A 2 dimensional array of SAT words

int nCorrect rand()3 //let's say 1
coutltlt"Which word has the definition "
ltltsaSATnCorrect1ltltendl
//Let's make A the correct answer
coutltlt"A "ltltsaSATnCorrect0ltltendl

column 0 1
accomplish
To bring to pass
row 0
adhere
To stick fast or together
row 1
amity
Friendship
row 2
61
A 2 dimensional array of SAT words

int nCorrect rand()3 //let's say 1
coutltlt"Which word has the definition "
ltltsaSATnCorrect1ltltendl
coutltlt"A "ltltsaSATnCorrect0ltltendl
//Now choose a random wrong answer
coutltlt"B "ltltsaSAT????ltltendl

column 0 1
accomplish
To bring to pass
row 0
adhere
To stick fast or together
row 1
amity
Friendship
row 2
62
A 2 dimensional array of SAT words

int nCorrect rand()3 //let's say 1
coutltlt"Which word has the definition "
ltltsaSATnCorrect1ltltendl
coutltlt"A "ltltsaSATnCorrect0ltltendl
coutltlt"B "ltltsaSATrand()30ltltendl

column 0 1
accomplish
To bring to pass
row 0
adhere
To stick fast or together
row 1
amity
Friendship
row 2
63
Problem There's a chance that the wrong answer
and the corrrect answer could be the same!

int nCorrect rand()3 //let's say 1
coutltlt"Which word has the definition "
ltltsaSATnCorrect1ltltendl
coutltlt"A "ltltsaSATnCorrect0ltltendl
coutltlt"B "ltltsaSATrand()30ltltendl

64
Problem There's a chance that the wrong answer
and the corrrect answer could be the same!

int nCorrect rand()3
int nWrong
do
nWrong ??
while(??)
coutltlt"Which word has the definition "
ltltsaSATnCorrect1ltltendl
coutltlt"A "ltltsaSATnCorrect0ltltendl
coutltlt"B "ltltsaSATnWrong0ltltendl

65
Problem There's a chance that the wrong answer
and the corrrect answer could be the same!

int nCorrect rand()3
int nWrong
do
nWrong rand()3
while(??)
coutltlt"Which word has the definition "
ltltsaSATnCorrect1ltltendl
coutltlt"A "ltltsaSATnCorrect0ltltendl
coutltlt"B "ltltsaSATnWrong0ltltendl

66
Problem There's a chance that the wrong answer
and the corrrect answer could be the same!

int nCorrect rand()3
int nWrong
do
nWrong rand()3
while(nWrong nCorrect)
coutltlt"Which word has the definition "
ltltsaSATnCorrect1ltltendl
coutltlt"A "ltltsaSATnCorrect0ltltendl
coutltlt"B "ltltsaSATnWrong0ltltendl

67
Practice Quiz Question What is the output of
this program?

include ltiostream.hgt
include ltstdlib.hgt
int Mystery(int nA, int nB)
int main (void)
int nY4, nZ3
coutltltMystery(nY,nZ)ltltendl
coutltltMystery(5,Mystery(nZ,nY))ltltendl
system("PAUSE")
return 0
int Mystery (int nA, int nB)
coutltlt"Hello"ltltendl
return nAnB

68
Practice Quiz Question What is the output of
this program?

include ltiostream.hgt
include ltstdlib.hgt
int Mystery(int nA, int nB)
int main (void)
int nY4, nZ3
coutltltMystery(nY,nZ)ltltendl
coutltltMystery(5,Mystery(nZ,nY))ltltendl
system("PAUSE")
return 0
int Mystery (int nA, int nB)
coutltlt"Hello"ltltendl
return nAnB

3
4
4
3
nA
4
nB
3
69
Practice Quiz Question What is the output of
this program?

include ltiostream.hgt
include ltstdlib.hgt
int Mystery(int nA, int nB)
int main (void)
int nY4, nZ3
coutltltMystery(nY,nZ)ltltendl
coutltltMystery(5,Mystery(nZ,nY))ltltendl
system("PAUSE")
return 0
int Mystery (int nA, int nB)
coutltlt"Hello"ltltendl
return nAnB

7
nA
4
nB
3
70
Practice Quiz Question What is the output of
this program?

include ltiostream.hgt
include ltstdlib.hgt
int Mystery(int nA, int nB)
int main (void)
int nY4, nZ3
coutltltMystery(nY,nZ)ltltendl
coutltltMystery(5,Mystery(nZ,nY))ltltendl
system("PAUSE")
return 0
int Mystery (int nA, int nB)
coutltlt"Hello"ltltendl
return nAnB

"Nested" function call
3
4
4
3
nA
3
nB
4
71
Practice Quiz Question What is the output of
this program?

include ltiostream.hgt
include ltstdlib.hgt
int Mystery(int nA, int nB)
int main (void)
int nY4, nZ3
coutltltMystery(nY,nZ)ltltendl
coutltltMystery(5,Mystery(nZ,nY))ltltendl
system("PAUSE")
return 0
int Mystery (int nA, int nB)
coutltlt"Hello"ltltendl
return nAnB

7
nA
nB
72
Practice Quiz Question What is the output of
this program?

include ltiostream.hgt
include ltstdlib.hgt
int Mystery(int nA, int nB)
int main (void)
int nY4, nZ3
coutltltMystery(nY,nZ)ltltendl
coutltltMystery(5,Mystery(nZ,nY))ltltendl
system("PAUSE")
return 0
int Mystery (int nA, int nB)
coutltlt"Hello"ltltendl
return nAnB

7
7
5
nA
5
nB
7
73
Practice Quiz Question What is the output of
this program?

include ltiostream.hgt
include ltstdlib.hgt
int Mystery(int nA, int nB)
int main (void)
int nY4, nZ3
coutltltMystery(nY,nZ)ltltendl
coutltltMystery(5,Mystery(nZ,nY))ltltendl
system("PAUSE")
return 0
int Mystery (int nA, int nB)
coutltlt"Hello"ltltendl
return nAnB

12
7
5
nA
5
nB
7
74
Pong
75
Pong
76
Pong

For many people, Pong was the first time they
used a computer
Brought the first computers into people's homes
Written by Alan Alcorn (a Lowell grad) for Atari
First Pong game was installed in a Sunnyvale bar
in September 1972
Two weeks later the machine stopped
workingbecause all the quarters had jammed it
Original Paddles had eight segmentsdifferent
segments gave different angles

77
The original arcade Pong game was basically some
logic chips hooked up to an actual TV set with an
added coin mechanism.
78
Pong was not the first computer game

10 years before Pong, there was another, much
more sophisticated computer game

79
Spacewar!
80
Spacewar!

Written by members of the MIT model railroad club
beginning in 1961
They also coined the word "hack"
Code was kept in an unlocked draweranyone was
free to modify it
Programmed on the Digital Equipment PDP-1, one of
the first computers with a monitor
Club members built the world's first joysticks
Later modified by Atari (stolen?) to become
Asteroids

81
Pong Spin-offs

Breakout 1976

82
Pong Spin-offs

Dr. Pong 1974

83
Pong Spin-offs

Pin Pong 1974

84
Pong Spin-offs

Pong Doubles 1973

85
Pong Spin-offs

Puppy Pong 1974

86
Pong Spin-offs

Quadra Pong 1974

87
Pong Spin-offs

Rebound 1974

88
Pong Spin-offs

Slime Volleyball

89
Pong Spin-offs

Bomb Bee 1979

90
Pong Spin-offs

Super Pong 1974

91
Pong Spin-offs

3d pong

92
Pong Spin-offs

circular pong

93
Pong Spin-offs

Warlords

94
Pong Spin-offs

and many, many others. . .

95
And from these humble beginnings

Computer gaming is now a huge industry with
revenue over 7 billion dollars in 2005
'Mario' has made twice the revenue of all the
'Star Wars' movies combined
Computer Games and entertainment software are the
fastest growing area of the computer software
industry (which is itself one of the fastest
growing areas of the economy)

96
Programming Pong

To keep things simple we'll write a single player
pong game
The main function will have the animation loop
There will be additional functions for moving,
drawing and erasing the paddle and ball

97
Starting with a "Bouncing Ball"

We'll build the program "Bottom Up"
Start with the "Bouncing Ball" and add the paddle
later

98
The "Bouncing Ball" Algorithm The Universal
Animation Loop

First, we want the ball to continue to move, even
if no key is pressed. The loop is
while(no key is pressed)
Erase the ball
Move the ball
Bounce the ball
Draw the ball
Wait

99
The Pong Ball Functions

void DrawBall(int nX,int nY)
void EraseBall(int nX,int nY)
void Move(int nX,int nY,
bool bGoingRight,bool bGoingDown)
void Bounce(int nX,int nY,
bool bGoingRight,bool bGoingDown)
Notice that nX, and nY are reference arguments in
Move, because they change
Likewise, bGoingRight, and bGoingDown are
reference arguments in Bounce

100
Adding a Paddle A loop inside of another loop

First, we'll keep the ball loop. . .and add
another loop around it
while(no key is pressed)
Erase the ball
Move the ball
Bounce the ball
Draw the ball
Wait

101
Adding a Paddle A loop inside of another loop

Then, if a key is pressed, we stop moving the
ball just long enough to take care of the paddle,
and then go back to moving the ball
do
while(no key is pressed)
Ball moving
Get the key pressed by the user
Erase the paddle
if the key pressed means "right"
Move the paddle to the right
else if it means "left"
Move the paddle to the left
Draw the paddle
while( key pressed does NOT mean "quit")

102
The Pong Paddle Functions

void DrawPaddle (int nX, int nY)
void ErasePaddle (int nX, int nY)

103
BallMasterwww.blueteagames.com
by Steven Zhao class of 2001 In BallMaster, you
guide a flying ball through dangerous adventures.
With the aid of your computerized assistant, you
fend off a variety of beasts that attack you as
you float through the air. Other Games Cactus
Bruce and the Corporate Monkeys, Meeklits and
HeliumMan-X
104
Using file input output to store the high score

Earlier in the course, we used redirection to
tell Windows (the OS) that input would come from
a data file
There is another technique where we can use C
to accomplish the same thing
If we are keeping score in Pong, we can store the
high score in a file

105
A program that gets a number and displays it to
the screen

include ltiostream.hgt
include ltstdlib.hgt
int main()
int nNum
cingtgtnNum
coutltlt"The number is "ltltnNumltltendl
system("PAUSE")
return 0

106
The same program modified to use file input

include ltiostream.hgt
include ltstdlib.hgt
include ltfstream.hgt
int main()
ifstream fin("input.txt")
if(!fin)
coutltlt"Error! file not found"ltltendl
else
int nNum
fingtgtnNum
coutltlt"The number is "ltltnNumltltendl
system("PAUSE")
return 0

107
file input

include ltfstream.hgt
Include the "file stream" library
ifstream fin("input.txt")
Declare the "input stream" and name it fin
Associate it with the file input.txt in the
Dev-C folder
if(!fin)
coutltlt"Error! file not found"ltltendl
Check to see if the file is there. The most
common problem in file input is a non-existent or
misplaced file.

108
Let's go back to our simple program that gets a
number and displays it to the screenNow we'll
modify it to use file output

include ltiostream.hgt
include ltstdlib.hgt
int main()
int nNum
cingtgtnNum
coutltlt"The number is "ltltnNumltltendl
system("PAUSE")
return 0

109
Let's go back to our simple program that gets a
number and displays it to the screenNow will
modify it to use file output

include ltiostream.hgt
include ltstdlib.hgt
include ltfstream.hgt
int main()
ofstream fout ("output.txt")
int nNum
cingtgtnNum
foutltlt"The number is "ltltnNumltltendl
system("PAUSE")
return 0

110
If we look inside the Dev-C folder after we run
the program, we should now see a file output.txt
with our output
111
file output

ofstream fout ("output.txt")
Declare an "output file stream" and call it fout
Associate it with a file called output.txt
Note output.txt will be created if it doesn't
already exist
foutltlt"The number is "ltltnNumltltendl
Use fout just like cout

112
A program that reads in the high score and
compares it with the current score

include ltiostream.hgt
include ltstdlib.hgt
include ltfstream.hgt
int main()
ifstream fin ("highscore.txt")
if(!fin)
coutltlt"Error! file not found"ltltendl
else
int nHighScore
int nScore 1000
fingtgtnHighScore
fin.close() //note that fin must be
closed
//before we can use the
same
//file for fout
if(nScore gt nHighScore)

113
Practice Quiz Questions

1. True/false The following is a correct
bounce function for Pong
if(nX gt 0)
bRight true
if(nX lt 640)
bRight false
if(nY gt 0)
bUp false
if(nY lt 480)
bUp true
2. If the function prototype is
void Bounce(int nX, int nY, bool bUp, bool
bRight)
then a correct call would be Bounce(nX,nY,bUp,bR
ight)
3.For
int naArray32 56, -17,
23, 45
22, 45
naArray12 is -17.
4. In the following code, nRand1 and nRand2 will
always be different
int nRand1 rand()100 1

114
What will be displayed?

void RandomNumber()
int main()
RandomNumber()
system("PAUSE")
return 0
void RandomNumber()
coutltltrand()ltltendl

115
What will be displayed now?

void RandomNumber()
int main()
RandomNumber()
system("PAUSE")
return 0
void RandomNumber()
coutltltrand()ltltendl
RandomNumber()

116
The program will repeatedly display random
numbersproblem is it won't stop!

void RandomNumber()
int main()
RandomNumber()
system("PAUSE")
return 0
void RandomNumber()
coutltltrand()ltltendl
RandomNumber()

117
Recursion A function that calls itself

void RandomNumber()
coutltltrand()ltltendl
RandomNumber()
Recursion is another way of making a loop
Recursion is hard to controlit's very easy to
create an infinite loop that never stops

118
In recursion, the "stopping point" is called the
base case

void RandomNumber(int nTimes)
if(nTimes 0)
coutltlt"Stop!"ltltendl
else
coutltltrand()ltltendl
RandomNumber(nTimes-1)
The base case stops the recursive calls

119

include ltiostream.hgt
include ltstdlib.hgt
void RandomNumber(int nTimes)
int main()
RandomNumber(5)
system("PAUSE")
return 0
void RandomNumber(int nTimes)
if(nTimes 0)
coutltlt"Stop!"ltltendl
else
coutltltrand()ltltendl
RandomNumber(nTimes-1)

120
Recursion

There are two basic ways to make things happen
"over and over again" in programming
Loops
Recursion
In theory, anything you can do with loops, you
can do with recursion ( vice versa)

121
A loop that "counts" from 1 to 10

int main()
for(int nI 1 nI lt 10 nI)
coutltltnIltltendl
system("PAUSE")
return 0

122
A Recursive Function that "counts" from 1 to 10

void RecursiveFunction(int nNum)
int main()
RecursiveFunction(1)
system("PAUSE")
return 0
void RecursiveFunction(int nNum)
if(nNum 10)
coutltltnNumltlt" and stop"ltltendl
else
coutltltnNumltltendl
RecursiveFunction(nNum1)

123
A Recursive Function calls itself

void RecursiveFunction(int nNum)
if(nNum 10)
coutltltnNumltlt" and stop"ltltendl
else
coutltltnNumltltendl
RecursiveFunction(nNum1)

124
Just like a loop, it has a starting point, a
stopping point, and a way to get from one to the
other

void RecursiveFunction(int nNum)
int main()
RecursiveFunction(1)//start at one
system("PAUSE")
return 0
void RecursiveFunction(int nNum)
if(nNum 10)//stop at 10
coutltltnNumltlt" and stop"ltltendl
else
coutltltnNumltltendl
RecursiveFunction(nNum1)//increment by 1

125
Recursion

Just like a loop, if recursion doesn't stop,
we'll crash the computer
void RecursiveFunction(int nNum)
if(nNum 10)
coutltltnNumltlt" and stop"ltltendl
else
coutltltnNumltltendl
RecursiveFunction(nNum1)
The if statement is called the base case
In the base case there is no recursive call, and
the recursion stops

126
What is the output?

int Mystery(int nNum)
int main()
coutltltMystery(4)ltltendl
system("PAUSE")
return 0
int Mystery(int nNum)
if(nNum lt 1)
return 1
else
return nNum Mystery(nNum - 1)

127
To understand, start with the base case

What would Mystery(1) return?
int Mystery(int nNum)
if(nNum lt 1)
return 1
else
return nNum Mystery(nNum - 1)

128
To understand, start with the base case

What would Mystery(1) return?
1
int Mystery(int nNum)
if(nNum lt 1)
return 1
else
return nNum Mystery(nNum - 1)

129
To understand, start with the base case

What would Mystery(1) return?
1
What would Mystery(2) return?
int Mystery(int nNum)
if(nNum lt 1)
return 1
else
return nNum Mystery(nNum - 1)

130
To understand, start with the base case

What would Mystery(1) return?
1
What would Mystery(2) return?
2 Mystery(1) 2 1 2
int Mystery(int nNum)
if(nNum lt 1)
return 1
else
return nNum Mystery(nNum - 1)

131
To understand, start with the base case

What would Mystery(1) return? 1
What would Mystery(2) return?
2 Mystery(1) 2 1 2
What would Mystery(3) return?
int Mystery(int nNum)
if(nNum lt 1)
return 1
else
return nNum Mystery(nNum - 1)

132
To understand, start with the base case

What would Mystery(1) return? 1
What would Mystery(2) return?
2 Mystery(1) 2 1 2
What would Mystery(3) return?
3 Mystery(2) 3 2 6
int Mystery(int nNum)
if(nNum lt 1)
return 1
else
return nNum Mystery(nNum - 1)

133
To understand, start with the base case

What would Mystery(4) return?
int Mystery(int nNum)
if(nNum lt 1)
return 1
else
return nNum Mystery(nNum - 1)

134
To understand, start with the base case

What would Mystery(4) return?
4 Mystery(3) 4 6 24
int Mystery(int nNum)
if(nNum lt 1)
return 1
else
return nNum Mystery(nNum - 1)

135
Recursion in the real world

Recursion is best used to model problems that can
be described recursively
Example Trees

136
Tree

A tree isn't made of just one branch or trunk

137
Tree

Each branch has smaller and smaller branches

138
Tree

Each branch has smaller and smaller branches

139
Tree

If you keep putting branches in at a smaller and
smaller scale, you can get a very interesting
tree (Broccoli?)

140
Recursion in Fern Leaves
141
This process of repeating the same design at a
continually decreasing scale is an example of a
Fractal
142
Problem write a program to display the first 20
fibonacci numbers

0,1,1,2,3,5,8,13,21,. . .

143
Problem write a program to display the first 20
Fibonacci numbers

0,1,1,2,3,5,8,13,21,. . .
after 0 and 1, each successive Fibonacci number
is the sum of the two previous Fibonacci numbers

144
Problem write a program to display the first 20
Fibonacci numbers

0,1,1,2,3,5,8,13,21,. . .
after 0 and 1, each successive Fibonacci number
is the sum of the two previous Fibonacci numbers

145
Problem write a program to display the first 20
Fibonacci numbers

int Fibonacci(int nNum)
int main()
for(int nI 0 nI lt 20nI)
coutltltFibonacci(nI)ltlt", "
system("PAUSE")
return 0
int Fibonacci(int nNum)
???

146
Problem write a program to display the first 20
Fibonacci numbers

What's the base case?
int Fibonacci(int nNum)
???

147
Problem write a program to display the first 20
Fibonacci numbers

What's the base case?
int Fibonacci(int nNum)
if(nNum 0)
return ??

148
Problem write a program to display the first 20
Fibonacci numbers

What's the base case?
int Fibonacci(int nNum)
if(nNum 0)
return 0
else if(nNum 1)
return ??

149
Problem write a program to display the first 20
Fibonacci numbers

From now on, add the two previous numbers
int Fibonacci(int nNum)
if(nNum 0)
return 0
else if(nNum 1)
return 1
else
return ??

150
Problem write a program to display the first 20
Fibonacci numbers

From now on, add the two previous numbers
int Fibonacci(int nNum)
if(nNum 0)
return 0
else if(nNum 1)
return 1
else
return Fibonacci(??)

151
Problem write a program to display the first 20
Fibonacci numbers

From now on, add the two previous numbers int
Fibonacci(int nNum)
if(nNum 0)
return 0
else if(nNum 1)
return 1
else
return Fibonacci(nNum - 1)
Fibonacci(nNum 2)

152
Problem write a program to display the first 20
Fibonacci numbers

include ltiostream.hgt
include ltstdlib.hgt
int Fibonacci(int nNum)
int main()
for(int nI 0 nI lt 20nI)
coutltltFibonacci(nI)ltlt", "
system("PAUSE")
return 0
int Fibonacci(int nNum)
if(nNum 0)
return 0
else if(nNum 1)
return 1
else
return Fibonacci(nNum-1)
Fibonacci(nNum-2)

153
Recursive Functions

A Recursive Function is a Function that calls
itself
int Mystery(int nNum)
if(nNum 0)
return 0
else
return 2 Mystery(nNum - 1)

154
Recursive Functions

A Recursive Function is a Function that calls
itself
int Mystery(int nNum)
if(nNum 0)
return 0
else
return 2 Mystery(nNum - 1)

Recursion
155
Recursive Functions

What would be returned by the call Mystery(0)?
int Mystery(int nNum)
if(nNum 0)
return 0
else
return 2 Mystery(nNum - 1)

0
0
156
Recursive Functions

What would be returned by the call Mystery(1)?
int Mystery(int nNum)
if(nNum 0)
return 0
else
return 2 Mystery(nNum - 1)

1
1
157
Recursive Functions

Mystery(1) 2 Mystery(0) 20
int Mystery(int nNum)
if(nNum 0)
return 0
else
return 2 Mystery(nNum - 1)

1
1
158
Recursive Functions

What would be returned by the call Mystery(2)?
int Mystery(int nNum)
if(nNum 0)
return 0
else
return 2 Mystery(nNum - 1)

2
2
159
Recursive Functions

Mystery(2) 2 Mystery(1)
2 2 Mystery(0) 2 2 0
int Mystery(int nNum)
if(nNum 0)
return 0
else
return 2 Mystery(nNum - 1)

2
2
160
Recursive Functions

What would be returned by the call Mystery(10)?

161
Recursive Functions

What would be returned by the call Mystery(10)?
Mystery(10) 2 Mystery(9)
22Mystery(8)
222Mystery(7)
2222Mystery(6)
22222Mystery(5)
222222Mystery(4)
2222222Mystery(3)
22222222Mystery(2)
222222222Mystery(1)
2222222222Mystery(0)20

162
Recursive Functions

Let's remove some code from Mystery
Now what would be returned by the call
Mystery(10)?
int Mystery(int nNum)
if(nNum 0) //delete 3 lines
return 0
else
return 2 Mystery(nNum - 1)

163
Recursive Functions

Mystery(10) 2 Mystery(9)
22Mystery(8)
222Mystery(7)
2222Mystery(6)
22222Mystery(5)
222222Mystery(4)
2222222Mystery(3)
22222222Mystery(2)
222222222Mystery(1)
2222222222Mystery(0)
22222222222Mystery(-1)
222222222222Mystery(-2)
and so on, and so on
Infinite Recursion! Stack Overflow!
CRASH!

164
The Base Case

Every recursive Function must have a base case
The base case is where the recursion stops
int Mystery(int nNum)
if(nNum 0) //base case
return 0
else
return 2 Mystery(nNum - 1)

165
More on break and continue

break and continue can be used to modify a loop
break immediately exits a loop
continue is somewhat the opposite, it "goes back
to the top" of the loop, skipping any remaining
code
Good Style whenever possible, avoid break and
continue, as they make code hard to understand

166
break