Chapter 8: Structure

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Chapter 8 Structure Enumeration

• In this chapter you will learn about,
• Introduction
• Defining a structure
• Declaring a structure variable
• Initialising structure elements
• Acessing structure elements
• Examples using structure
• Defining enumeration constants
• Declaring enumeration variable
• Examples using enumeration

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Introduction

• So far we have only used
• Basic data types, such as int, float, double and
  char.
• Array
• String (which is an array of characters)
• The concept of structure is similar to array in
  the sense that both store a group of elements.
• However, in an array, all the elements are of the
  same data type but in a structure, the data can
  be of different data types.
• A structure can contain basic data types, arrays
  and even another structure.

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Defining a Structure

• General syntax
• struct structure_name
• data_type element1
• data_type element2
• . . .
• Example
• struct student
• char name20
• int studentID
• char major50

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Declaring Structure Variables

• After defining a structure, we may declare
  variables that are of that structure. A
  structure variable declaration requires
• The keyword struct
• The structure type name
• A list of elements (variable names) separated by
  commas
• A concluding semicolon
• For example, to declare a variable my_student of
  type structure student, it should be written as
  follow.
• struct student my_student
• struct student my_stud, your_stud

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Declaring Structure Variables

• By including this declaration in our program, we
  are informing the compiler about a new structure
  defined by the user.
• The declaration makes the compiler aware of the
  existence of the structure does not take an
  action yet.
• As a result of the declaration, sufficient memory
  space for variable my_student, which includes the
  components of its structure, will be reserved.

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Declaring Structure Variables
Conceptual memory structure variable my_student
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Declaring Structure Variables

• It is possible to combine the declarations of a
  structure and its variable by including the name
  of the variable at the end of the structure
  declaration.
• struct student
• char name20
• int studentID
• char major50
• struct student my_student

struct student char name20 int
studentID char major50 my_student
?
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Nested Structure

• It is possible for a structure to have another
  structure as one of its components/elements.
• Consider the following structure declaration
• struct address
• int no
• char street20
• int zipcode

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Nested Structure

• We can rewrite the structure student declaration
  to include structure address as one of its
  elements as follow.

struct student char name20 int
studentID char major50 struct address
addr my_student
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Declaring Nested Structure cont

• The updated structure student can also be written
  as below.
• struct student
• char name20
• int studentID
• char major50
• struct address
• int no
• char street20
• int zipcode
• addr
• my_student

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Accessing Structure Elements

• A structure contains many elements. Each element
  of a structure can be accessed using the
  structure variable name followed by the . (dot)
  operator followed by the element name.
• Let us use the structure student which we have
  seen before as an example.

struct student char name20 int
studentID char major50 my_student
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Accessing Structure Elements

• Therefore, to access the elements of a
  my_student, we write as follow
• my_student.name
• my_student.studentID
• my_student.major
• Therefore, to assign values to the element of the
  structure, we write
• my_student.studentID 10179

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Initialising Structure Elements

• Just like array and other types of variables, we
  can initialise a structure while we are declaring
  an instance of the structure. For example,
• struct student my_student "Ahmad", 10179,
  "IT"
• Notice that it is possible to use the
  operator on a struct variable. When the sign
  is used, each value on the right will be
  respectively copied into the structure components
  according to their declaration in the structure
  definition.

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Example 1

• struct birthdate
• int mon
• int day
• int yr
• struct birthdate me 10, 25, 1881
• printf("I was born on d/d/d\n", me.day,
  me.mon, me.yr)

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Example 2
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Array of structures
includeltstdio.hgt struct birthdate int
mon int day int yr void
main(void) struct birthdate me5 for (i0
ilt5 i) printf("Enter day") scanf("d",
mei.day) printf("Enter month") scanf("d",
mei.mon) printf("Enter year") scanf("d",
mei.yr)
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Enumeration Constants

• An enumeration, introduced by the keyword enum,
  is a set of integer constants represented by
  identifiers.
• Example definition
• enum islamic_months
• muharam, safar, rabiulawal, rabiulakhir,
• jamadilawal, jamadilakhir, rejab, syaaban,
• ramadhan, syawal, zulkaedah, zulhijjah
• Each of the identifiers will have a corresponding
  integer constant value that starts with 0 (unless
  specified otherwise). Therefore, we can treat
  them as integers.

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Enumeration Constants

• If we want the enumeration to start with a value
  other than 0, we can assign the value to the
  first identifier
• enum islamic_months
• muharam 1, safar, rabiulawal, rabiulakhir,
• jamadilawal, jamadilakhir, rejab, syaaban,
• ramadhan, syawal, zulkaedah, zulhijjah
• Just like structure, before an enumeration can be
  used, an enumerated variable needs to be
  declared
• enum islamic_months my_months

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Enumeration Constants

• Enumeration constants basically makes your
  program more readable.
• There are cases where it is appropriate for us to
  use an enumeration. For example,
• enum islamic_months my_months
• scanf("d", my_months)
• switch (my_months)
• case muharam
• . . .
• break
• case safar
• . . .
• break
• case ramadhan printf(lunch not provided)
• break

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Enumeration Constants

• This is another case where it is more appropriate
  to use an enumeration.
• enum Boolean FALSE, TRUE
• void main ( )
• int number 5, key
• Boolean found
• printf("Enter number ")
• scanf("d", key)
• if (number key)
• found TRUE
• else
• found FALSE

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Example
include ltstdio.hgt enum months JAN 1, FEB,
MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT, NOV,
DEC void main ( ) enum months month char
monthsName "January","February","March","Ap
ril","May","June", "July","August","September","O
ctober","November", "December" for (month
JAN month lt DEC month) printf("d s",
month, monthNamemonth-1)
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Example

• Output
• 1 January
• 2 February
• 3 March
• April
• May
• June
• July
• August
• September
• October
• November
• December

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Summary

• This chapter you learned about structures
• Structure definition and structure variable
  declaration
• Initialising structure elements
• Accessing structure elements
• Defining, declaring and using enumeration
  constants