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.
Enter…the 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; … };

7. This would go above main()
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
firstName ID
lastName
GPA
lastName
GPA

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.ID=333;
Bill.GPA=3.87;
cout<<Bill.ID;
cin>>Bill.lastName;
Bill
firstName ID
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, who’s 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
lastName
GPA

11. Aggregate Operations (performed on a struct as a whole)
Assignment
Arithmetic
Comparison
Passing Arguments
Return from a function
Allowed on Structs? No
Yes
Yes, value and reference
Operations labelled ‘no’ can still be performed on a field by field basis (see next slide)

12. Example How to do the operations on StudentRec x, y;
Assignment
Arithmetic
Comparison
Passing to Fn
Function return
Correct Example
cin>>x.firstName>>x.lastName
>>x.ID>>x.GPA; (Wrong: cin>>x)
y=x; (copies all fields) or x.ID=y.ID
y.GPA=x.GPA+y.GPA; (Wrong: x=x+y)
if (x.ID < y.ID) (Wrong: if (x<y))
Display(x); OR y.GPA=sqrt(x.GPA)
return x; OR return x.GPA

13. Initializing Structs
When a struct is created you can initialize it with a list of values (initialization list): StudentRec s={“Isa”, “Corwin”,3.5, 555};
The sequence must match the order of declaration in the
struct (see slide 7):
NO: StudentRec s={“Isa”,“Corwin”,555,3.5};OOPS
You can only do this on declaring
StudentRec t;
NO: t={“Bert”,“Lance”,3.5, 555}; ERROR

14. Data Abstraction
Data abstraction is the separation of a data’s logical properties from its implementation, for example: Logical 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!)

15. TRY IT NOW!! Prepare for Project 2, Part 2
Practice basic concepts of structs by completing Assignment 11, problems 1-7