The structure construct is to represent multi-part objects where each part is named. Consider the pseudo code.
Class person:
creation()
first name:=" "
last name:=" "
id :=" "
email:=" "
The new data type Person is pictorially represented as

We can now represent a rational number as a pair of two integers in pseudo code:
numerator(x):
return x[0]
denominator (x):
return x[1]

The structure construct is to represent multi-part objects where each part is named. Consider the pseudo code.
Class person:
creation()
first name:=" "
last name:=" "
id :=" "
email:=" "
The new data type Person is pictorially represented as

(i) A concrete data type is a data type whose representation is known.
(ii) Direct implementations of a relatively simple concept.

The square bracket notation is used to access the data stored in the pair. The data is Zero indexed, meaning we access the first element with nums[0] and the second with nums[1].
nums:=(1,2)
nums[0]
1
nums[1]
2

A pair is a compound data type that holds two other pieces of data. So far, we have provided with two ways of representing the pair data type. The first way is using list construct and the second way to implement pairs is with the tuple construct.

Tuple is similar to a list. The difference between the two is that you cannot change the elements of a tuple once it is assigned whereas in a list, elements can be changed.

A Pair is a compound data type that holds two other pieces of data. We have provided two ways of representing the pair data type. The first way is using list construct and the second way to implement pairs is with the tuple construct. List can be called as pairs because list bundles two values together into one as a pair.

The elements of a list can be accessed in the method of multiple assignments, which unpacks a list into its elements and binds each element to a different name.
1st:=[10,20]
x,y:=1st
In the above example, x will become 10 and y will become 20. Mathematically we can represent list similar to a set.
Example:
lst [(0,10), (1,20)]

An ADT for rational numbers:
- - constructor
- - constructs a rational number with numerator n, denominator d
rational(n, d)
- - selector
number(x) \(\rightarrow \) returns the numerator of rational number x
denom(y) \(\rightarrow \) returns the denominator of rational number y

(i) Data abstraction is supported by defining an abstract data type (ADT) which is a collection of constructors and selectors.
(ii) Constructors create an object, bundling together different pieces of information, while selectors extract individual pieces of information from the object.

(i) Constructor
(ii) Selector
(iii) Constructor
(iv) Selector
(v) Selector