COMP102 Session 3A

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COMP102 Session 3A

• Lab10 Guessing the Capitals

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Character Strings

• A sequence of characters
• Referred to as a character string
• Stored in an array of type char
• Ending
• With the null character
• '\0'

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Character Strings

• A character string is a sequence of characters
  enclosed in double quotes
• E.g.
• char s12 a
• char message12 Hello world

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getline

• Member function of cin
• Get a character string from input
• E.g.

char lastName30, firstName30 cin.getline(la
stName, sizeof(lastName), ',') cin.getline(firstN
ame, sizeof(firstName))
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String Copy Function

• Include ltstring.hgt
• Copies source string into destination string
• void strcpy(char dest, const char src)
• E.g.
• char str16
• strcpy(str, Hello World)

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String Length Check Function

• Include ltstring.hgt
• Returns length of string
• int strlen(const char)
• Not including \0
• E.g.
• int string_length strlen("abcde")
• strncpy(str_1, str_2, strlen(str_1))

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String Comparison

• Compares strings s1 and s2
• int strcmp(char s1, char s2)
• if (s1 lt s2)
• Return -1
• if (s1 s2)
• Return 0 (false)
• if (s1 gt s2)
• Return 1
• int strncmp(char s1, char s2, int limit)
• Same as strcmp
• Except that at most limit characters are compared

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Common Errors

• Illegal to use to assign value to a string
  variable
• Except at declaration
• char str6 Hello
• E.g.
• str Hello
• Use strcpy function instead
• strcpy(str, Hello)

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Common Errors

• The operator doesn't test two strings for
  equality
• E.g.
• if (string1 string2)
• Use strcmp function instead
• if (!strcmp(string1, string2))

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Structure

• Structure User defined data types
• Collection of related data items
• Possibly of different types
• In C
• Called struct
• Can be composed of data of different types
• Array
• Can contain only data of the same type

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Structure

• E.g.
• Student record
• Student id, name, major, gender, start year,
• Bank account
• Account number, name, currency, balance,
• Address book
• Name, address, telephone number,

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Structure

• Individual components of a struct type
• Called members (or fields)
• Members can be of different types
• int, float, double, char, array, or even another
  struct
• A struct is named as a whole
• While individual members are named using field
  identifiers
• Complex data structures
• Can be formed by defining arrays of structs

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struct Basics

• Definition of a structure
• E.g.

struct ltstruct-typegt lttypegt
ltidentifier_listgt lttypegt ltidentifier_listgt

struct date int day int month int
year
struct studentRecord char gender int
id char dept5 char name20
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struct Basics

• Declaration of a variable of struct type
• Syntax
• ltstruct-typegt ltidentifier_listgt
• E.g.
• studentRecord student1, student2
• student1 and student2 are variables of
  studentRecord type

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struct Basics

• The members of a struct type variable are
  accessed with the dot (.) operator
• Syntax
• ltstruct-variablegt.ltmember_namegt
• E.g.
• student1.gender 'M'
• student1.id 12345
• strcpy(student1.dept, "COMP")
• strcpy(student1.name, "Chan Tai Man")

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struct Basics

• Overview

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struct-to-struct Assignment

• The values contained in one struct type variable
• Can be assigned to another variable
• Of the same struct type
• E.g. student1 student2
• E.g.

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Nested Structures

• Nest structures inside structures
• E.g.

struct point double x, ypoint
Pstruct line point p1, p2line
Lstruct triangle point p1, p2,
p3triangle T
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Arrays of Structures

• An array of structs
• Multiple types of data in each array element
• E.g.

studentRecord class100class98.gender
'M'class98.id 12345strcpy(class98.dept,
"COMP")strcpy(class98.name, "Chan Tai
Man")class0 class98
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Arrays inside structures

• We can use arrays inside structures
• E.g.
• Assign values to sq using the given square

struct square point vertex4 square
sq
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Initialize Data of struct Type

• Using assignment during declaration
• E.g.

// student record struct StudentRecord
double totalgrade char namename_size
char idid_size int gradeno_grades
StudentRecord student1 0.0, "CHAN Tai
Man", "123456", 80, 67, 34, 67
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Enumerated Type

• The enumerated type (enum)
• Derived from the integer type
• Each integer value is given an identifier
• Called an enumeration constant
• Syntax
• enum type_name enumeration_constants
• type_name variable_name

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Enumerated Type

• E.g.

enum days mon, tue, wed, thur, fri, sat,
sun days day_of_week // normal expression
day_of_week wed // ERROR miss match type
day_of_week 0 // CORRECT 0 is converted to
days day_of_week (days) 0 // Use
enumeration constant as an integer int x
tue // same as x 3 int day7
daytue 0 // same as day1 0
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enum and struct

• E.g.

enum suit club, diamond, heart, spade struct
card suit cardSuit int value