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SE Computer- Division A

Course Name :Principles of Programming Language

Course Code: 210256

Course InCharge: Parag Achaliya

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Unit 2

Structuring the Data, Computations and Program

Elementary Data Types : Primitive data Types, Character String types, User Defined Ordinal Types, Array types, Associative Arrays, Record Types, Union Types, Pointer and reference Type.
Expression and Assignment Statements: Arithmetic expression, Overloaded Operators, Type conversions, Relational and Boolean Expressions, Short Circuit Evaluation, Assignment Statements, Mixed mode Assignment.
Statement level Control Statements: Selection Statements, Iterative Statements, Unconditional Branching.
Subprograms: Fundamentals of Sub Programs, Design Issues for Subprograms, Local referencing Environments, Parameter passing methods. Abstract Data Types and Encapsulation Construct: Design issues for Abstraction, Parameterized Abstract Data types, Encapsulation Constructs, Naming Encapsulations

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Data type: A data type defines a collection of data values and

a set of predefined operations on those values

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An object represents an instance of a user-defined (abstract data) type

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Primitive Data Types

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Primitive Data Types

Primitive data types are those that are not defined in terms of other data types

Early PLs had only numeric primitive types, and still play a central role among the collections of types supported by contemporary languages.

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Numerical Data Types …Integer

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Numerical Data Types …Floating Point

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Numerical Data Types …Floating Point

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Numerical Data Types …Decimal

Advantage

Accuracy

Disadvantages:

Limited range
Wastes memory

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Boolean Types

Advantage: � Readability

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Character Types

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Character String Types

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Character String Types …. String Operations

Character string type is one in which the values consist of sequences of characters

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Character String Types.. String Length Options

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Character String Types

C and C++

not primitive
use char arrays and a library of functions that provide operations

Java : String class (not arrays of char)

objects are immutable
StringBuffer is a class for changeable string objects
String length options

Static – Python, Java’s String class, C++ standard class library, Ruby’s built-in String class, and the .NET class library in C# and F#.
Limited dynamic length – C and C++ ( up to a max length indicated by a null character)
Dynamic –Perl, JavaScript

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Used Defined Ordinal Types

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An ordinal type is one in which the range of possible values can be easily associated with the set of positive integers

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Enumeration Types

All possible values, which are named constants, are provided in the definition
C# example

enum days {mon, tue, wed, thu, fri, sat, sun};

The enumeration constants are typically implicitly assigned the integer values, 0, 1, …, but can be explicitly assigned any integer literal in the type’s definition

Design issues

Is an enumeration constant allowed to appear in more than one type definition, and if so, how is the type of an occurrence of that constant checked?
Are enumeration values coerced to integer?
Any other type coerced to an enumeration type?

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Subrange Type

An ordered contiguous subsequence of an ordinal type

Not a new type, but a restricted existing type

Example: 12..18 is a subrange of integer type

Introduced by Pascal and included in Ada

Ada’s design

type Days is (Mon, Tue, Wed, Thu, Fri, Sat, Sun);

subtype Weekdays is Days range Mon..Fri;

subtype Index is Integer range 1..100;

Day1: Days;

Day2: Weekday;

Day2 := Day1; //legal if Day1 it not set to Sat or Sun

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Array Type

An array is an aggregate of homogeneous data elements in which an individual element is identified by its position in the aggregate, relative to the first element.

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Array and Indexes

Indexing (or subscripting) is a mapping from indices to element

array_name (index_value_list) -> element

Index Syntax

FORTRAN, PL/I, Ada use parentheses , Sum-:= Sum +B(I);
Ada explicitly uses parentheses to show uniformity between array references and function calls because both are mappings
Most other languages use brackets
E.g. List(27) direct reference to the List array’s element with the subscript 27.

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Array and Indexes

Language	Index Type
FORTRAN , C, Java	Integer
PASCAL	Any Ordinal Type (Integer, Boolean, Enumeration, Character)
Ada	Integer Or Enumeration

C, C++, Perl, and Fortran do not specify range checking
Java, ML, C# specify range checking

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Categories of Arrays

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Categories of Arrays

Static: subscript ranges are statically bound and storage allocation is static (before run‐ time)
Advantage: efficiency (no dynamic allocation/deallocation required)
Example: In C and C++ arrays that include the static modifier are static
static int myarray[3] = {2, 3, 4};
int static_array[7];

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Array Initialization

Some language allow initialization at the time of storage allocation

Fortran

List (3) Data List /0, 5, 5/ // List is initialized to the values

C, C++, Java, C# example

int list [] = {4, 5, 7, 83}

Character strings in C and C++

char name [] = “freddie”; // eight elements, including last element as null character

Arrays of strings in C and C++

char *names [] = {“Bob”, “Jake”, “Joe”];

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Array Initialization

Some language allow initialization at the time of storage allocation
Java initialization of String objects

String[] names = {“Bob”, “Jake”, “Joe”};

Ada positions for the values can be specified:

List : array (1..5) of Integer := (1, 3, 5, 7, 9);

Bunch : array (1..5) of Integer:= (1 => 3, 3 => 4, others => 0);

Note: the array value is (3, 0, 4, 0, 0)

Concatenation. One array can be appended to another array using the & operator provided that they are of the same type.

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Array Operations

Language	Array Operation
C-based	No Operations , only through methods
C#, Perl	Array Assignments
Ada	Assignment, Concatenation(&), Comparison
Python	Concatenation(+), Element Membership(in), Comparison(==, is)
FORTRAN	Matrix Multiplication, Transpose
APL(Most powerful)	+.* ,

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Associative Array

An associative array is an unordered collection of data elements that are indexed by an equal number of values called keys
Also known as Hash tables

Index by key (part of data) rather than value
Store both key and value (take more space)
Best when access is by data rather than index

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Associative Array

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Record Type

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Record Type

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Union

A union is a type whose variables are allowed to store different type values at different times during execution
Design issues

Should type checking be required?
Should unions be embedded in records?

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Pointer and reference type

A pointer type variable has a range of values that consists of memory addresses and a special value, nil
Provide the power of indirect addressing
Provide a way to manage dynamic memory
A pointer can be used to access a location in the area where storage is dynamically created (usually called a heap)

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Pointer Operations

Two fundamental operations: assignment and dereferencing
Assignment is used to set a pointer variable’s value to some useful address
Dereferencing yields the value stored at the location represented by the pointer’s value
Dereferencing can be explicit or implicit
C++ uses an explicit operation via *

j = *ptr

sets j to the value located at ptr

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Pointer Assignment Illustrated

The assignment operation

j = *ptr

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Expressions are the fundamental means of specifying computations in a programming language.
To understand expression evaluation, need to be familiar with the orders of operator and operand evaluation.
The purpose of assignment variable is to change the value of variable.

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Introduction to Expression

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Arithmetic evaluation was one of the motivations for the development of the first programming languages.

Arithmetic expressions consist of operators, operands, parentheses, and function calls.

Operators can be:

A unary operator has one operand.

A binary operator has two operands.

A ternary operator has three operands.

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Arithmetic Expression

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Unary Arithmetic Operators in C/C++ and Java

Unary Plus ( +A ):

Examples: +num, +num/5, num1 * +num2

Has no effect on its operand in C/C++.

In Java, it causes an implicit conversion of a char, short, or byte operand to int type; otherwise, it has no effect on its operand.

Unary Minus ( -A ):

Examples: -num, -num/5, num1 * -num2

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Unary Arithmetic Operators in C/C++ and Java (cont.)

The pre-increment is specified as follows: (++a)

It says to add 1 to the current value of the variable and then to use the new value (if necessary).

The post-increment is specified as follows: (a++)

It says to use the current value of the variable (if necessary) and then add 1 to it.

The pre-decrement is specified as follows: (--a)

It says to subtract 1 from the current value of the variable and then to use the new value (if necessary).

The post-decrement is specified as follows: (a--)

It says to use the current value of the variable (if necessary) and then subtract 1 from it.

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Binary Arithmetic Operators in C/C++ and Java

Operation	Operator	Example	Operand	Result
Addition	+	A + B	Both integers ------------------- One operand is not integer	Integer ------------------ Double precision floating-point
Subtraction	-	A – B	Both integers ---------------------------- One operand is not integer	Integer ----------------------- Double precision floating-point
Multiplication	*	A * B	Both integers ------------------------------ One operand is not integer	Integer ------------------------- Double precision floating-point
Division	/	A / B	Both integers ------------------------------ One operand is not integer	Integer ------------------------- Double precision floating-point
Modulus (Remainder)	%	A % B	Both integers	Integer

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Ternary Operator in C/C++ and Java

A ternary operator “ ?: ” has three operands.

average = (a>b)? a : b;

Evaluates as if written like:

if (a>b) average = a;

else average = b;

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Arithmetic Expressions :Conditional Expressions

Conditional Expressions:

C-based languages (e.g., C, C++).

An example:

average = (a>b)? a : b;

Evaluates as if written like:

if (a>b) average = a;

else average = b;

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Overloaded Operators

Operator Overloading is accomplished by defining functions that have the same name as the operator being overloaded.

Some are common (e.g., +, -, *, … for int and float).

C++, FORTRAN 95 and Ada allow user-defined overloaded operators.

Java does not permit operator overloading.

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Overloaded Operators - division operator issue

avg= sum/count
Avg is floating point but sum and count are integer
The result gives integer value for Avg

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Explicit Type Conversions

Explicit Type Conversions:

Called casting in C-based language.

Examples:

C conversion (cast)

int a, b;� float x;� x = (float)a/(float)b;

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Relational and Boolean Expressions

Relational operators in various languages:

Ada: =, /=, >, <, >=, <=
Java: ==, !=, >, <, >=, <=

Relational operators always have lower precedence than arithmetic operators.
Relational Expressions:

Use relational operators and operands of various types.
Evaluate to some Boolean representation.

Boolean Expressions:

Operands are Boolean and the result is Boolean.
C/C++ operators: &&, ||, !
C has no Boolean type, it uses int type with 0 for false and nonzero for true.

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Short-Circuit Evaluation

A short-circuit evaluation of an expression is one in which the result is determined without evaluating all of the operands and/or operators.

Types:

In Arithmetic Expressions:

Ex.: (13*a) * (b/13–1)

If a is zero, there is no need to evaluate (b/13-1).

In logical Expressions:

Ex.: The value of (a >= 0) and (b < 10) is independent of the second relational expression if a < 0.

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Assignment Statements

The general syntax:

<target_var> <assign_operator> <expression>

The assignment operator:

= FORTRAN, BASIC, PL/I, C, C++, Java.

:= ALGOLs, Pascal, Ada.

Simple assignment:

a = b;
a = b = c;

Suppose a, b, and c are integers.
In C, the integer value of c is assigned to b, which is in turn assigned to a (multiple targets).

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Assignment statements (cont.)

Unary assignment operators:

count++;
++count;
sum = ++count; 🡺 count incremented then assigned to sum
sum = count++; 🡺 count assigned to sum then incremented

Assignment as an expression:

In C, C++, and Java the assignment statement produces a result and can be used as operands.

while ((ch = getchar()) != EOF) { … }

ch = getchar() is carried out; the result (assigned to ch) is used as a conditional value for the while statement.

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Selection Statements

A selection statement provides the means of choosing between two or more paths of execution
Two general categories:

Two-way selectors
Multiple-way selectors

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Iterative Statements

The repeated execution of a statement or compound statement is accomplished either by iteration or recursion
General design issues for iteration control statements:

1. How is iteration controlled?

2. Where is the control mechanism in the loop?

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while (ctrl_expr)

loop body

do

loop body

while (ctrl_expr)

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Fundamentals of Subprograms

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Fundamentals of Subprograms

Each subprogram has a single entry point
The calling program is suspended during execution of the called subprogram
Control always returns to the caller when the called subprogram’s execution terminates

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Basic Definitions

A subprogram definition describes the interface to and the actions of the subprogram abstraction
A subprogram call is an explicit request that the subprogram be executed
A subprogram header is the first part of the definition, including the name, the kind of subprogram, and the formal parameters
The parameter profile (aka signature) of a subprogram is the number, order, and types of its parameters
The protocol is a subprogram’s parameter profile and, if it is a function, its return type

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Basic Definitions

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Design Issues for Subprograms

What parameter passing methods are provided?
Are parameter types checked?
Are local variables static or dynamic?
Can subprogram definitions appear in other subprogram definitions?
Can subprograms be overloaded?
Can subprogram be generic?

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Local Referencing Environments

Variables that are defined inside subprograms are called local variables.
Local variables can be either static or stack dynamic
“bound to storage when the program begins execution and are unbound when execution terminates.”

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Parameter Passing Methods

Ways in which parameters are transmitted to and/or from called subprograms

Pass-by-value
Pass-by-result
Pass-by-value-result
Pass-by-reference
Pass-by-name

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Abstract Data Type and Encapsulation Constructs

Design issues for Abstraction,
Parameterized Abstract Data types,
Encapsulation Constructs,
Naming Encapsulations

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The Concept of Abstraction

An abstraction is a view or representation of an entity that includes only the most significant attributes
The concept of abstraction is fundamental in programming (and computer science)
Nearly all programming languages support process abstraction with subprograms
Nearly all programming languages designed since 1980 support data abstraction

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Introduction to Data Abstraction

An abstract data type is an enclosure that includes only the

data representation of one specific data type and
the subprograms that provide the operations for that type

An instance of an abstract data type is called an object.

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Design Issues for Abstract Data Types

What is the form of the container for the interface to the type?
Can abstract types be parameterized?
What access controls are provided?

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Parameterized Abstract Data Types

Parameterized ADTs allow designing an ADT that can store any type elements (among other things) – only an issue for static typed languages
Also known as generic classes
C++, Ada, Java 5.0, and C# 2005 provide support for parameterized ADTs

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Encapsulation Constructs

Large programs have two special needs:

Some means of organization, other than simply division into subprograms
Some means of partial compilation (compilation units that are smaller than the whole program)

Obvious solution: a grouping of subprograms that are logically related into a unit that can be separately compiled (compilation units) Such collections are called encapsulation

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Naming Encapsulations

Large programs define many global names need a way to divide into logical groupings
A naming encapsulation is used to create a new scope for names

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