Variables

1
Basic C Programming
Review

• Variables
• and
• Special Chars
• (Ch. 2, 3)

2
Valid Variable Names

• Rules for variable names in C (page 33)
• The first character must be an alphabetic
  character or underscore
• Consists only of alpha-numeric and underscore
  characters
• Cannot duplicate a reserved word (see Appendix B)

Invalid Names a for 2name a
a int
Valid Names a PI student_name
_PI _assign1
3
Important Special Characters
As a Character In a String

• Return \n
• Null
• Single Quote
• Double Quote
• Backslash

\n \0 \ \ \\
\n \ \\
4
Constant declarations

• Constants are used to store values that never
  change during the program execution.
• Using constants makes programs more readable and
  maintainable.
• Syntax
• const lttypegt ltidentifiergt ltexpressiongt
• Examples
• const double US2HK 7.8
• //Exchange rate of US to HK
  
• const double HK2TW 3.98
• //Exchange rate of HK to TW
  
• const double US2TW US2HK HK2TW
• //Exchange rate of US to TW
  

5
Variable declarations

• Variables are used to store values that can be
  changed during the program execution.
• A variable is best thought of as a container for
  a particular type of data/value.
• You must specify the variables type when you
  declare it
• Syntax
• lt type gt lt identifier gt
• lt type gt lt identifier gt lt expression gt
• Examples
• int sum
• int i j 0
• int total 3445
• char answer 'y'
• double temperature -3.14

6
Variable declarations

• Variables are not automatically initialized. For
  example, after declaration
• int sum
• the value of the variable sum can be anything
  (garbage).
• Thus, it is good practice to initialize variables
  when they are declared.
• A variable has a type and it can contain only
  values of that type. For example, a variable of
  the type int can only hold integer values.
• Once a value has been placed in a variable it
  stays there until the program deliberately alters
  it.

7
Character data

• A variable or a constant of char type can hold an
  ASCII character (see Appendix A of the textbook).
  
• When initializing a constant or a variable of
  char type, or when changing the value of a
  variable of char type, the value is enclosed in
  single quotation marks.
• Examples
• const char star ''
• char letter, one '1'

8
Programming

• Decisions
• (Ch. 5)

9
The Basic if Statement

• Syntax
• if(Expression)
• Action
• If the Expression is true then execute Action
• Action is either a single statement or a group of
  statements within braces

10
Choice (if)

• Example find the absolute value
• if (value lt 0)
• value -value
• Can put multiple action statements within braces
• if ltit's raininggt
• lttake umbrellagt
• ltwear raincoatgt

11
Sorting Two Numbers
int value1 int value2 int temp cout ltlt "Enter
two integers " cin gtgt value1 gtgt
value2 if(value1 gt value2) temp
value1 value1 value2 value2 temp cout
ltlt "The input in sorted order " ltlt value1
ltlt " " ltlt value2 ltlt endl
12
Relational Operators

• Relational operators are used to compare two
  values
• Math C Plain English
• equals example if(ab)
• BUT (ab) means put the value of b into a
• lt lt less than
• ? lt less than or equal to
• gt gt greater than
• ? gt greater than or equal to
• ? ! not equal to

13
A Boolean Type

• C contains a type named bool which can have one
  of two values
• true (corresponds to non-zero value)
• false (corresponds to zero value)
• Boolean operators can be used to form more
  complex conditional expressions
• The AND operator is
• The OR operator is
• The NOT operator is !
• Warning
• and are bitmap operators

14
More Operator Precedence

• Precedence of operators (from highest to lowest)
• Parentheses ( )
• Unary operators !
• Multiplicative operators /
• Additive operators -
• Relational ordering lt lt gt gt
• Relational equality !
• Logical and
• Logical or
• Assignment

15
Examples of bool

• Assignments to bool type variables
• bool P truebool Q falsebool R
  truebool S P Q // Fbool T !Q R //
  T bool U !(R !Q) // F

16
Operator Precedence Examples

• Examples
• 5 ! 6 7 lt 3
• is equivalent to
• (5 !6) (7 lt 3)
• 5 15 4 13 12 lt 19 !false 5 lt 24
• is TRUE

17
The if-else Statement
Syntax if (Expression) Action1 else
Action2 ? If Expression is true then execute
Action1 otherwise execute Action2
18
The if-else Statement

• if ltit's sunnygt
• ltgo to beach with sun blockgt
• else
• lttake umbrellagt

19
Finding the Big One
int value1 int value2 int larger cout ltlt
"Enter two integers " cin gtgt value1 gtgt
value2 if (value1 gt value2) larger
value1 else larger value2 cout ltlt "Larger
is " ltlt larger ltlt endl
20
if-else-if Statements
F
T
F
T
F
T
F
T
21
if-else-if Statements

• if ltMon, Wedgt
• ltgoto COMP 103gt
• else if ltTuegt
• ltgoto Labgt
• else if lt12noon or 7PMgt
• lteatgt
• else
• ltsleepgt

22
if-else-if Statement

• if(score gt 90)
• cout ltlt "Grade A" ltlt endl
• else if(score gt 80)
• cout ltlt "Grade B" ltlt endl
• else if(score gt 70)
• cout ltlt "Grade C" ltlt endl
• else if(score gt 60)
• cout ltlt "Grade D" ltlt endl
• else
• cout ltlt "Grade F" ltlt endl

23
switch Statement

• Equivalent to the previous if-else-if
• switch(score/10)
• case 10
• case 9 cout ltlt "Grade A" ltlt endl
• break
• case 8 cout ltlt "Grade B" ltlt endl
• break
• case 7 cout ltlt "Grade C" ltlt endl
• break
• case 6 cout ltlt "Grade D" ltlt endl
• break
• default cout ltlt "Grade F" ltlt endl

24
Nested if Statements

• Nested means that one complete statement is
  inside another
• if ltit's Mondaygt
• if ltit's 100pmgt
• if ltit's raininggt
• ltbring umbrellagt
• ltgo to COMP 103gt
• ltcall your friendsgt

25
Dangling Else Problem

• What is the value of c after the following is
  executed?
• int a-1, b1, c1
• if(agt0)
• if(bgt0)
• c 2
• else
• c 3
• C groups a dangling else with the most recent
  if (answer c1).

26
Programming

• Functions
• (Ch. 4)

27
Advantages of Functions

• A complex problem is often easier to solve by
  dividing it into several smaller parts, each of
  which can be solved by itself.
• These parts are called functions in C
• Functions make programs easier to understand.
• Functions make programs easier to modify.
• Functions can be called several times in the same
  program, allowing the code to be reused.

28
Function Input and Output

29
Functions in a Program

• C programs usually have the following form
• // include statements
• // function prototypes
• // main() function
• // user-defined functions

30
Function Prototype

• The function prototype declares the interface, or
  input and output parameters of the function,
  leaving the implementation for the function
  definition.
• The function prototype has the following syntax
• lttypegt ltfunction namegt(lttype listgt)
• Example A function that prints the card (J)
  given the card number (11) as input
• void printcard(int num)
• (This is a void function - a function that does
  not return a value)

31
Function Definition

• The function definition can be placed anywhere in
  the program after the function prototypes.
• You can place a function definition in front of
  main(). In this case there is no need to provide
  a function prototype for the function, since the
  function is already defined before its use.
• A function definition has following syntax
• lttypegt ltfunction namegt(ltparameter listgt)
• ltlocal declarationsgt
• ltsequence of statementsgt

32
Function Call

• A function call has the following syntax
• ltfunction namegt(ltparameter listgt)
• There is a one-to-one correspondence between the
  parameters in a function call and the parameters
  in the function definition.

33
Printing Cards (void function)

• The main() program which calls printcard()
• include ltiostreamgt
• using namespace std
• void printcard(int) // function prototype
• int main()
• int c1, c2, c3, c4, c5
• // pick cards
• . . .
• // print cards
• printcard(c1)
• printcard(c2)
• printcard(c3)
• printcard(c4)
• printcard(c5)
• // find score
• // print score

34
Printing Cards

• A function that prints the card (J) given the
  card number (11) as input
• void printcard(int cardnum)
• if(cardnum1)
• cout ltlt "A"
• else if(cardnumgt2 cardnumlt10)
• cout ltlt cardnum
• else if(cardnum11)
• cout ltlt "J"
• else if(cardnum12)
• cout ltlt "Q"
• else if(cardnum13)
• cout ltlt "K"

35
Absolute Value (returns int)

• include ltiostreamgt
• int absolute(int x) // function prototype
• int main()
• int x, y, diff
• cout ltlt "Enter two integers "
• cin gtgt x gtgt y
• diff absolute(x - y)
• cout ltlt "The absolute diff is " ltlt diff ltlt
  endl
• return 0
• // Define a function to take absolute value of an
  int
• int absolute(int x)
• if (x gt 0) return x
• else return -x

36
Passing Parameters by Value

• A function returns a single result (assuming the
  function is not a void function)
• One of the statements in the function body should
  have the form
• return ltexpressiongt
• The value passed back by return should have the
  same type as the function.

37
Pass by Value

• Different location in memory

• Changes to the parameters inside the function
  body have no effect outside of the function.

38
Pass by Value Example 1

• For example, consider the following code
• int sum(int a, int b)
• a a b
• return a
• void main()
• int x, y, z
• x 3 y 5
• z sum(x,y)
• What is the value of x, y, and z at the end of
  the main() program?

39
Pass by Value Example 1

• The answer 3, 5, and 8. (x,y,z)
• Even though the value of parameter a is changed,
  the corresponding value in variable x does not
  change.
• This is why this is called pass by value.
• The value of the original variable is copied to
  the parameter, but changes to the value of the
  parameter do not affect the original variable.
• In fact, all information in local variables
  declared within the function will be lost when
  the function terminates.
• The only information saved from a pass by value
  function is in the return statement.

40
Pass by Value Example 2

• void Increment(int Number)
• Number Number 1
• cout ltlt "Number " ltlt Number ltlt endl
• void main()
• int I 10
• cout ltlt "I is " ltlt I ltlt endl
• Increment(I)
• cout ltlt "I is " ltlt I ltlt endl

41
Passing Parameters by Reference

• To have a function with multiple outputs, we have
  to use pass by reference.
• Reference (address) of parameter is passed to the
  function, instead of its value.
• If the function changes the parameter value, the
  changes will be reflected in the program calling
  it.
• How to pass parameters by reference
• lttypegt ltvariablegt, ... , lttypegt ltvariablegt

42
Pass by Reference Example

• The correct implementation of the Increment
  function
• include ltiostreamgt
• using namespace std
• void Increment(int Number)
• Number Number 1
• cout ltlt "Number " ltlt Number ltlt endl // 11
• void main()
• int I 10
• Increment(I)
• cout ltlt "I is " ltlt I ltlt endl // 11
• Pass-by-Reference-1.cpp

43
Example Exchange two numbers
If we use pass by value, it will not work!!!

• a and num1 are in the same location in memory
• Also b and num2

44
Pass by value and by reference
45
Programming

• Loops
• (Ch. 6)

46
Iterative Constructs

• Provide
• Ability to control how many times a statement
  list is executed
• Three constructs
• while statement
• for statement
• do-while statement

47
The while Statement

• Syntax
• while (Expression)
• Action
• How it works
• If Expression is true then execute Action
• Repeat this process until Expression evaluates to
  false
• Action is either a single statement or a group of
  statements within braces

48
Example N! (while)

• int number, factorial, n
• cout ltlt "Enter number "
• cin gtgt number
• factorial 1
• n 1
• while(n lt number)
• factorial n
• n
• cout ltlt "The factorial of " ltlt number
• ltlt " is " ltlt factorial ltlt endl

49
The for Statement

• Syntax
• for (ForInit ForExpression PostExpression)
• Action
• How it works
• Execute ForInit statement
• As long as ForExpression
• is true
• Execute Action
• Execute PostExpression

50
Example N! (for)

• int number, factorial, n
• cout ltlt "Enter number "
• cin gtgt number
• factorial 1
• for (n1 nltnumber n)
• factorial n
• cout ltlt "The factorial of " ltlt number
• ltlt " is " ltlt factorial ltlt endl

51
The Do-While Statement

• Syntax
• do Action
• while (Expression)
• How it works
• Execute Action
• if Expression is true then execute Action again
• Repeat this process until Expression evaluates to
  false
• Action is either a single statement or a group of
  statements within braces

52
Example N! (do-while)

• int number, factorial, n
• cout ltlt "Enter number "
• cin gtgt number
• factorial 1
• n 1
• do
• factorial n
• n
• while(n lt number)
• cout ltlt "The factorial of " ltlt number
• ltlt " is " ltlt factorial ltlt endl

53
Which Loop to Use?

• For loop
• Usually best for sums, products, and counting
  loops.
• While loop
• You want to repeat an action without knowing
  exactly how many times it will be repeated.
• There are situations when the action should not
  be executed.
• Do-while loop
• The action should always be executed at least
  once.
• Otherwise, the do-while loops and while loops are
  used in similar situations.

54
How to Stop a Loop

• Known number of iterations before the loop stops
  (for)
• Test for a user-controlled
• condition before or after
• each iteration (while, do-while)
• Use the break command.

55
Stop a loop break

• The break command is the same as the one used
  previously in switch.
• break leaves the current loop immediately. It is
  recommended that break be used for situations
  where the loop needs to be terminated immediately
  (e.g., due to user intervention or if a fatal
  error occurs).
• Use with care !!

56
Example Maximum (while with break)
int value //input value int max0 //maximum
value while(true) cout ltlt "Enter a value (-1
to stop) " cin gtgt value if(value gt
max) max value if(value-1) break
cout ltlt "The maximum value found is " ltlt " is
" ltlt max ltlt endl
57
Common Loop Errors

• while(balance ! 0.0)
• balance balance - amount
• This will lead to an infinite loop!
• for(n1 nltcount n)
• cout ltlt "hello" ltlt endl
• "hello" only printed once!
• while(balance ! 0.0)
• balance balance - amount
• balance may not become equal zero due to
  numerical inaccuracies

58
Nested Loops

• Nested loops are loops within loops.

// Program to output the // multiplication
table int i //Outer loop counter int
j //Inner loop counter for(i1 ilt10
i) for(j1 jlt10 j) cout ltlt ij ltlt "
" cout ltlt endl
Output 1 2 3 4 5 6 7 8 9 10 2 4 6 8 10 12 14 16
18 20 3 6 9 12 15 18 21 24 27 30
59
Programming

• Recursion
• (Ch.6, Section 6-9)

60
Recursion

• Recursion is one way to decompose a task into
  smaller subtasks.
• The smallest example of the same task has a
  non-recursive solution.
• Example The factorial function
• n! n (n-1) (n-2) ... 1
• or
• n! n (n-1)! and 1! 1
• A recursive solution may be simpler to write
  (once you get used to the idea) than a
  non-recursive solution.
• But a recursive solution may not be as efficient
  as a non-recursive solution of the same problem.

61
Recursion General Form

• How to write recursively?
• int rec(parameters)
• if(stopping condition)
• return stopping value
• value rec(revised parameters)
• return value

62
Example N! Recursion

• int fac(int n)
• int product
• if(n lt 1)
• return 1
• product n fac(n-1)
• return product
• void main()
• int number 3
• cout ltlt fac(number) ltlt endl

63
Execution trace

• fac(3)
• 3 lt 1 ? No.
• product3 3 fac(2)
• fac(2)
• 2 lt 1 ? No.
• product2 2 fac(1)
• fac(1)
• 1 lt 1 ? Yes.
• return 1
• product2 2 1 2
• return product2
• product3 3 2 6
• return product3
• fac(3) has the value 6

64
Programming

• Arrays

65
Arrays

• An array is a collection of data elements that
  are of the same type (e.g., a collection of
  integers, collection of characters, collection of
  doubles).

66
Arrays

• 1-dimensional array.
• 3-dimensional array (3rd dimension is the day).

67
Array Declaration 1 Dimension

• Syntax lttypegt ltarrayNamegtltdimensiongt

68
Subscripting 1 Dimension

• // array of 10 uninitialized ints
• int A10
• A3 1
• int x A3

69
Array Initialization 1 Dimension
70
Example Definitions 1 Dimension

• Suppose
• const int N 20
• const int M 40
• const int MaxStringSize 80
• const int MaxListSize 1000
• Then the following are all legal array
  definitions.
• int A10 // array of 10 ints
• char BMaxStringSize // array of 80 chars
• double CMN // array of 800 doubles
• int ValuesMaxListSize// array of 1000 ints

71
Example Smallest Value (1-dimension)

• const int N10
• int AN
• int SmallestValueSoFar, i
• ... // A is input by user
• SmallestValueSoFar A0
• for (i1 iltN i)
• if (Ai lt SmallestValueSoFar)
• SmallestValueSoFar Ai

72
2-D Array Example
int table54
73
Programming

• Passing Arrays to Functions
• (Ch.8, p.388-397)

74
Passing Array Elements
Individual elements can be passed to a function
like ordinary values.
75
Passing Arrays as Parameters

• Arrays can be passed to functions in their
  entirety.
• All that is required is the address of the first
  element and dimensions of the array.
• The remainder of the array will be passed by
  reference automatically.
• Using in the formal parameter specification
  indicates that the variable is an array.

76
Example Multiple an array by 2
77
The const type modifier

• If the function must not change any element of
  the array then const should be used in the formal
  parameter specification of that array.

78
Passing Multidimensional Arrays

• How to pass a multidimensional array to a
  function
• void displayBoard(int b4)
• // function prototype requires variable name for
  arrays
• void main()
• int board 44
• ...
• displayBoard(board)
• ...
• void displayBoard(int b4)
• // could also be void displayBoard(int
  b44)
• // but NOT void displayBoard(int b)
• ...
• When passing a multidimensional array, only the
  size of the 1st dimension is optional, the 2nd,
  3rd, etc. dimensions must be specified.

79
Programming

• Structures
• (Ch.11, p.567)

80
Structures

• A structure is a collection of related data
  items, possibly of different types.
• In C, structure is a user defined type, called
  struct.
• A struct is heterogeneous (of different types of
  data) whereas an array is homogeneous (of same
  type of data)
• Examples
• Student record
• student id, name, major, gender, start year,
• Bank account
• account number, name, currency, balance,
• Address book
• name, address, telephone number,
• In database applications, structures are called
  records.

81
struct basics

• Definition of a structure
• struct ltstruct-typegt
• lttypegt ltidentifier_listgt
• lttypegt ltidentifier_listgt
• ...
• Example
• struct Date
• int day
• int month
• int year

Each identifierdefines a memberof the
structure.
The Date structure has 3 members, day,
month year.
82
struct examples

• Example
• struct BankAccount
• char Name15
• int AcountNo10
• double balance
• Date Birthday
• Example
• struct StudentRecord
• char Name15
• int Id
• char Dept5
• char Gender

The BankAcount structure has simple, array
and structure types as members.
The StudentRecord structure has 4 members.
83
struct basics

• Declaration of a variable of struct type
• ltstruct-typegt ltidentifier_listgt
• Example
• StudentRecord Student1, Student2
• Student1 and Student2 are variables of
  StudentRecord type.

Student1
Student2
84
Example 1 struct basics

• The members of a struct type variable are
  accessed with the dot (.) operator
• ltstruct-variablegt.ltmember_namegt
• Example
• strcpy(Student1.Name, "Chan Tai
  Man")Student1.Id 12345strcpy(Student1.Dept,
  "COMP")Student1.gender 'M'cout ltlt "The
  student is "switch (Student1.gender) case
  'F' cout ltlt "Ms. " break case 'M' cout ltlt
  "Mr. " breakcout ltlt Student1.Name ltlt endl

Student1
85
Example 2 struct-to-struct assignment

• The value of one struct type variable can be
  assigned to another variable of the same struct
  type.
• Example
• strcpy(Student1.Name, "Chan Tai
  Man")Student1.Id 12345strcpy(Student1.Dept,
  "COMP")Student1.gender 'M'Student2
  Student1

Student1
Chan Tai Man 12345 M COMP
Chan Tai Man 12345 M COMP
Student2
86
Example 3 Nested structures

• We can nest structures inside structures.
• Examples
• struct point double x, ypoint Pstruct
  line point p1, p2line Lstruct triangle
  point p1, p2, p3triangle T

(P.x, P.y)
(L.p2.x, L.p2.y)
(L.p1.x, L.p1.y)
(T.p2.x, T.p2.y)
(T.p3.x, T.p3.y)
(T.p1.x, T.p1.y)
87
Example 4 Nested structures

• We can nest structures inside structures.
• struct line point p1, p2line L

(L.p2.x, L.p2.y)
(L.p1.x, L.p1.y)
88
Arrays of structures

• An ordinary array One type of data
• An array of structs Multiple types of data in
  each array element.

89
Arrays of structures

• ExampleStudentRecord Class100strcpy(Class98
  .Name, "Chan Tai Man")Class98.Id
  12345strcpy(Class98.Dept, "COMP")Class98.g
  ender 'M'Class0 Class98

90
Arrays inside structures

• We can use arrays inside structures.
• Examplestruct square point vertex4squar
  e Sq
• Assign values to Sq using the given square

(4, 3)
(10, 3)
(4, 1)
(10, 1)
x y
x y
x y
x y