SOFTWARE DEVELOPMENT IN C CM9041

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SOFTWARE DEVELOPMENT IN CCM904-1

• Lecture 5
• Searching and sorting
• Data Structures

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This week

• Structs
• Typedef
• Searching
• Sorting
• Examples using structs

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Parallel Arrays
Corresponding position in each array refers to a
different piece of data which is an item of data
belonging to the same logical entity e.g.
Name (string) Age (integer) Grade
(character) Number of Attendances (int)
0 1 2 3 4 5
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Data Collections Involving Multiple Types

• Requires of an array of structures capable of
  holding complex data. Referred to in C as a
  struct
• Each element of the array contains a collection
  of data of the same format.

Name Age Grade Attendances
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Array of Structs
An array of structs
Name Age Grade Attendances
Name Age Grade Attendances
Name Age Grade Attendances
Name Age Grade Attendances
0 1 2 3
Studentarr2
Studentarr0
The definition of each element is referred to as
a Struct
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Arrays of Structs

• A Struct is a collection of data variables under
  one name
• Each constituent variable may be of a different
  data type
• Each part of the Struct can be accessed directly
• A Struct is user-defined
• Variables are declared as being instances of the
  user-defined type in the same way that variables
  of pre-defined types are declared (using a
  slightly different notation however!!)
• An array can be composed of Structs to give an
  indexed collection of objects that consist of
  mixed data
• studentarray1 student (copy a struct into a
  position in an array)
• studentarray1.age 21 (update part of an
  element of an array of structs

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Defining a struct
Here is an example structure definition.
typedef struct char name64, course128
int age, year student This
defines a new type student. Variables of type
student can then be declared as
follows. student st_record
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Arrays of Structures

• An array called birthdays of the same data type
  as the structure date can be created thus
•  
• struct date birthdays5
•  
• This creates an array of 5 elements each of type
  date.
• Assignments and operations can be carried out
  thus e.g
• birthdays1.month 12
• --birthdays1.year

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Variations in declaring structures

• struct date
• int month, day, year
• todaysdate, purchase_date  
• struct date
• int month, day, year
• todaysdate 25,9,1985
• struct date
• int month, day, year
• dates100

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Structures containing structures

• Structures can also contain structures.
•  
• struct date
• int month, day, year
•  
• struct time
• int hours, mins, secs
•  
• struct date_time
• struct date sdate
• struct time stime

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typedef

• A way of identifying a programmer-defined data
  type
• Avoids proceeding all struct declarations with
  the word struct
• Allows struct to be passed as a parameter into a
  function
• Variables can be created of a type once it has
  been defined using typedef

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Searching and sorting

• Lists of data often stored in arrays
• May be complex data
• Use arrays of structs
• Many standard processes require searching and
  sorting

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Linear Search

• Suitable for sorted or unsorted list
• Starts at beginning of array and checks each
  element against a target
• Loops for number of items in the list
• Returns position in array of found item or value
  representing not found
• Position used to retrieve data

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Linear Search

• Target value 10

Index 0
Index 1
Index 2
Index 3

• Position found 3

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Linear Search

• Target value 101

Index 0
Index 1
Index 2
Index 3
Index 4
1
34
28
10
9
81
1
34
28
10
9
81
Index 5

• Position found -1

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Searching an array of structs

• Same process
• Use one of the fields to search
• e.g. birthdayslistindex.month
• Returns position in array as before

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Bubble Sort

• Sort needed for variety of reasons
• Can be ascending or descending
• Sorted data often required for more efficient
  searching algorithms
• Bubble sort one of the simplest
• Each complete pass results in the highest
  unsorted item bubbling to the end.

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First Pass
Compare 0,1
Compare 1,2
Compare 2,3
Compare 3,4
Compare 4,5
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Second Pass
Compare 0,1
Compare 1,2
Compare 2,3
Compare 3,4
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Third Pass
Compare 0,1
Compare 1,2
Compare 2,3
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Sorting array of structs

• Same principle as for single data arrays
• One of the fields is used to perform the
  comparison
• E.g.
• birthdays i.month gt
• birthdaysi1.month
• If a swap is needed the whole structs are swapped

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Next week

• More on functions
• Introduction to pointers
• Passing data between functions
• Assignment help