Lec17 Structs

1
Lec17 Structs
2
Review of Data Types

• float floating point numbers
• int integer numbers
• char single ASCII character
• string a class representing a sequence of
  characters
• ifstream, ofstream classes representing pathways
  to files

3
These are great but somewhat limited

• How would you represent an automobile in a
  computer?
• What about an ATM bank account?
• An employee entry in a database?
• And so on
• We need a type that goes beyond simple one type
  data.
• Enterthe struct!!

4
Structured Data Types

• A structured data type is one in which each value
  is a collection of components and whose
  organization is characterized by the method used
  to access individual components (i.e. the dot .
  operator)

5
Structs

• A record or a struct in C, is a structured data
  type with a fixed number of components that are
  accessed by name. The components may be
  heterogeneous (mixed types).
• A field or component is a piece of the record.

6
Syntax of struct definition

• struct TypeName
• DataType MemberName
• DataType MemberName

7
Example StudentRec

• struct StudentRec
• string firstName
• string lastName
• float GPA
• int ID

This would go above main()
8
Creating StudentRec variables

• Once you declare a struct StudentRec, it becomes
  a new data type you can use
• StudentRec Bill, Tamara

Bill
Tamara
firstName
ID
ID
firstName
GPA
lastName
GPA
lastName
9
Accessing a field

• To assign a value to one of the fields, you use
  the member selector operator .
• StudentRec Bill // create a variable of type
  StudentRec
• Bill.firstName William
• Bill.lastName Borroughs
• Bill.ID333
• Bill.GPA3.87
• coutltltBill.ID
• cingtgtBill.lastName

Bill
ID
firstName
William
333
GPA
lastName
3.87
Borroughs
10
Your turn

• Declare a student record for a variable x
• Make x store the data for Kalina Noori, whos ID
  is 456 and GPA is 3.97
• Display the first and last names of x on the same
  line
• Input the ID and GPA of x

x
ID
firstName
GPA
lastName
11
Aggregate Operations (performed on a struct as a
whole)

• Aggregate Operation
• I/O
• Assignment
• Arithmetic
• Comparison
• Passing Arguments
• Return from a function

• Allowed on Structs?
• No
• Yes
• No
• No
• Yes, value and reference
• Yes

Operations labelled no can still be performed
on a field by field basis (see next slide)
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Example How to do the operationson StudentRec x,
y

• Operation
• I/O
• Assignment
• Arithmetic
• Comparison
• Passing to Fn
• Function return

• Correct Example
• cingtgtx.firstNamegtgtx.lastName
• gtgtx.IDgtgtx.GPA (Wrong cingtgtx)
• yx (copies all fields) or x.IDy.ID
• y.GPAx.GPAy.GPA (Wrong xxy)
• if (x.ID lt y.ID) (Wrong if (xlty))
• Display(x) OR y.GPAsqrt(x.GPA)
• return x OR return x.GPA

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Initializing Structs

• When a struct is created you can initialize it
  with a list of values (initialization
  list)StudentRec sIsa, Corwin,3.5, 555
• The sequence must match the order of declaration
  in the
• struct (see slide 7)
• NO StudentRec sIsa,Corwin,555,3.5?OOPS
• You can only do this on declaring
• StudentRec t
• NO tBert,Lance,3.5, 555 ?ERROR

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Data Abstraction

• Data abstraction is the separation of a datas
  logical properties from its implementation, for
  exampleLogical Properties of a real number
• addition, multiplication, positive, negative
• Implementation of a real number
• Hardware, limited bits, mantissa, exponent
• how these can be used to provide adding,
  multiplication
• An Abstract Data Type is a data type whose
  properties are specified independently of any
  particular implementation. How we represent real
  things on a computer
• This leads us to Classes (2 weeks!)

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TRY IT NOW!!

• Prepare for Project 2, Part 2
• Practice basic concepts of structs by completing
  Assignment 11, problems 1-7