**31. Parenthesis is never required in Postfix or Prefix expressions, why?**

**Ans:**Parenthesis is not required because the order of the operators in the postfix /prefix expressions determines the actual order of operations in evaluating the expression

**32. Minimum number of queues needed to implement the priority queue?**

**Ans:**Two. One queue is used for actual storing of data and another for storing priorities.

**33. Whether Linked List is linear or Non-linear data structure?**

**Ans:**According to Storage Linked List is a Non-linear one.

**34. What is the data structures used to perform recursion?**

**Ans:**Stack. Because of its LIFO (Last In First Out) property it remembers its ‘caller’ so knows whom to return when the function has to return. Recursion makes use of system stack for storing the return addresses of the function calls.

Every recursive function has its equivalent iterative (non-recursive) function. Even when such equivalent iterative procedures are written, explicit stack is to be used.

**35. What does abstract Data Type Mean?**

**Ans:**Data type is a collection of values and a set of operations on these values. Abstract data type refer to the mathematical concept that define the data type.

It is a useful tool for specifying the logical properties of a data type.

ADT consists of two parts

1) Values definition

2) Operation definition

**Example:-**The value definition for the ADT RATIONAL states that RATIONAL value consists of two integers, second doesn’t equal to zero.

The operator definition for ADT RATIONAL includes the operation of creation (make rational) addition, multiplication and test for equality.

**36. What are the notations used in Evaluation of Arithmetic Expressions using prefix and postfix forms?**

**Ans:**Polish and Reverse Polish notations.

37. What are the major data structures used in the following areas : network data model & Hierarchical data model.

37. What are the major data structures used in the following areas : network data model & Hierarchical data model.

**Ans:**

RDBMS – Array (i.e. Array of structures)

Network data model – Graph

Hierarchical data model – Trees

**38. Sorting is not possible by using which of the following methods?**

(a) Insertion

(b) Selection

(c) Exchange

(d) Deletion

(a) Insertion

(b) Selection

(c) Exchange

(d) Deletion

**Ans:**(d) Deletion.

Using insertion we can perform insertion sort, using selection we can perform selection sort, using exchange we can perform the bubble sort (and other similar sorting methods). But no sorting method can be done just using deletion.

**39. List out few of the applications that make use of Multilinked Structures?**

**Ans:**Sparse matrix, Index generation.

**40. Convert the expression ((A + B) * C – (D – E) ^ (F + G)) to equivalent Prefix and Postfix notations.**

**Ans:**Prefix Notation:

^ – * +ABC – DE + FG

Postfix Notation:

AB + C * DE – – FG + ^