Extra Lecture: Project 2 Structs

1
Extra LectureProject 2 Structs
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Did you do Project 2 Part 1 yet?

• Part 1 (8 Points) This part should be completed
  after Lecture9.ppt
• Start by writing a program, Proj2v1.cpp that
  reads and calculates drug doses for all the
  patients in file PatientData.dat. The output data
  is just displayed to the screen, using proper
  output formatting for evenly spaced, justified
  columns. (Note, strings need to be converted to
  c_strings for the setw( ) format command to work
  on them in Bloodshed, for example,
  coutltltsetw(15)ltltname.c_str( ) )

3
Part1 Read File, calc/display info

• Sample output (first 2 lines out of 25)
• Trenton Reba 27
• Masengill Fortuna 24
• You'll need to use a function to calculate and
  return the drug dose based on a patient's data.
  (Note you are only calculating one drug dose per
  patient). This function, CalcDose( ) will use a
  basic dose rate for adults of 0.2 mg per pound of
  body weight for patients over 120 pounds.
  Patients under 120 pounds will use a dose rate of
  1200.2 or 24 mg. In addition, girls aged 12 and
  under will only be given 25 of the adult dose
  calculated above, while boys 16 and under will be
  given 75 of the adult dose. The final drug dose
  will be rounded using the Round function from
  Lecture6.ppt.

4
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

5
These are great but somewhat limited

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

6
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)
• See p 296 section 12.9 (inserted after classes)

7
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.

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Syntax of struct definition

• struct TypeName
• DataType MemberName
• DataType MemberName

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Example StudentRec

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

This would go above main()
10
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
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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
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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
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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 (next week!)

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TRY IT NOW!!

• Work on Project 2
• Part 1 doesnt need structs at all
• Part 2 needs to use a struct for Patient data
• If you need help understanding structs, try doing
  exercises in structs.doc and structs.cpp