Abstract Data Type (ADT)
Abstract Data Type (ADT)
• An Abstract Data Type (ADT) is a data
structure with a set of operations
– Operations specify how the ADT behaves, but does
not reveal how they are implemented
– In many cases, there are more than one way to
implement an ADT
• In this course we will cover lots of ADTs
Trees & Search Trees
Hash Tables & Tries
Abstract Data Type (ADT) - more
• An Abstract Data Type (ADT) is a data
structure with a set of operations
Attributes (ADT State)
Operations (ADT Methods)
• What is a list?
List ADT
– An ordered sequence of elements A1, A2, …, AN
– Elements may be of arbitrary, but the same type
(i.e., all ints, all doubles etc.)
• Common List operations are:
Insert(ElementType E, Position P)
Delete(Position P)
Find(ElementType E)
IsEmpty() – Returns true if the list is empty
First() – Returns the first element
Last() – Returns the last element
Kth(Position K) – Returns the Kth element
Length() – Returns the length of the list
Array List ADT
ArrayList ADT
#define MAX_SIZE 100;
typedef struct ArrayList {
int elements[MAX_SIZE];
int noOfElements;
// Constructor:
// Make empty list
noOfElements = 0;
} // end-ArrayList
ArrayList (); // Constructor
void Insert(int e, int pos);
void Delete(int pos);
int Find(int e);
bool IsEmpty();
int First();
int Last();
int Kth(int pos);
int Length();
The Abstract Data Type (ADT)
The concept of abstraction means:
• We know what a data type can do
• How it is hidden for the user
With an ADT users are not concerned with how the task is
done but rather with what it can do.
ADT: Example
• The program code to read/write some data
is ADT. It has a data structure (character,
array of characters, array of integers,
array of floating-point numbers, etc.) and a
set of operations that can be used to
read/write that data structure.
The Abstract Data Type (ADT)
The Abstract Data Type (ADT) is:
• A data declaration packaged together with the operations that
are meaningful for the data type.
• In other words, we encapsulate the data and the operations on
the data, and then we hide them from the user.
Declaration of data
Declaration of operations
Encapsulation of data and operations
The Abstract Data Type (ADT)
• All references to and manipulation of the data in a structure must
be handled through defined interfaces to the structure.
• Allowing the application program to directly reference the data
structure is a common fault in many implementations.
• We must hide the implementation from the user
ADT Operations
Several classes of operations are required in
order to effectively used ADT.
1. Constructors – used to create instances of the
data type.
2. Destructors – used to destroy an instance of the
data type
3. Accessors – used to access attributes of the
data type. (Such as “get” functions)
4. Modifiers – used to modify attributes of the
data type. (Such as “set” functions)
Object-oriented languages provide some of this
functionality within the language. In C you must do it
While we’ve defined an ADT interface, we
can’t just start coding quite yet. There
are more design decisions to be made
before writing code for the
A common error among programmers is to not
place enough emphasis on the design step.
This is the difference between a
“programmer” and an “analyst”.
Fraction ADT Design: Data
Analysis begins with the idea that all the operations will be acting on Fractions
that have some internal representation. The representation shall be shared
among all the operations.
Each operation is responsible for maintaining your design rules regarding the
representation of Fraction information.
typedef enum{ POS, NEG } SignType;
typedef Fraction {
// data members
int numerator;
/* numerator and denominator are declared as */
int denominator; /* int to simplify the algorithms, but they */
SignType sign;
/* will always be stored >= 0
// public:
// member functions would follow
// utility functions would follow
All operations must preserve these rules.
Fraction ADT Variables
• Now that we’ve decided how to represent
the value of a fraction, how are we going to
declare variables whose values are
Fraction f1, f2;
Fraction ADT Algorithms
• You are responsible for designing
algorithms that implement all the
operations. What process must you follow
to implement the operations?
ad + bc
Sum:  +  =
 * = 
then, reduce
then, reduce
Subtraction involves adding the opposite, and
Division involves multiplying by the reciprocal.
Fraction ADT Algorithms
• Reducing a fraction involves finding the Greatest
Common Divisor, and then dividing all the terms by
that amount.
Euclid’s Algorithm:
if x < y, then swap x and y
While y is not zero
remainder = x mod y
y = remainder
When you’re done, x is the GCD.
/*********** Accessors
int getNumerator();
int getDenominator();
char getSign();
/********** Modifiers ***********/
void setNumerator(int);
void setDenominator(int);
void setSign(char);
void reduceFract();
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