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Data Types

Data types are a crucial concept in programming, defining the types of data and the operations they can perform. Different data types such as integers, floating-point numbers, strings, etc. have different storage methods and value ranges to meet the different needs of the program. Choosing and using data types correctly is the key to writing efficient and reliable code. This is a mind map about the Data Types chapter. The map is divided into three main branches according to chapters, namely: Basic Overview, User Defined Ordinal, and Data Types. Each main branch has a detailed description of its sub branches. Suitable for people interested in Data Types.

編輯於2024-04-28 17:19:55

Asmaa

Data Types

Asmaa

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Lecture 2 - Unit 1 : Data Types

Basic Overview

Definition Data Type : Defines a collection of data values and a set of predefined operations on those values.

Importance of providing appropriate data types and data structures.

User-defined types allow modifiability

Abstract data types hide their internal implementation and present only an interface to the users.

Uses of type system :

- Error detection

- Program modularization (cross module type checking)

- Documentation

Type system of a language defines how a type is associated with each expression in the language and includes rules for type equivalence and type compatibility .

descriptor is a collection of attributes of a variable .

Data Types

Character String Types

is one in which the value contains a collection of characters .

Design issues:

1- Should strings be a character array or a primitive type?

2- Should strings have static or dynamic length?

Operations

Most common operations : 1-Assignment. 2- Concatenation. 3-Substring. 4-Reference. 5-Comparison. 6-Pattern matching.

C and C++ > char arrays to store strings.

Most commonly used String library functions :strcpy, strcat, strcmp and strlen.

Java

provides : String, StringBuffer and StringBuilder classes .

C# and Ruby similar string classes like = Java.

Python: string as a primitive type and are immutable

F# : Strings are classes.

ML : String as a primitive type and are immutable.

Built-in Pattern Matching , include : Perl, JavaScript, Ruby and PHP

Ex : /[A-Za-z][A-Za-z\d]+/ -Matches : "A123", "aBc456", "Xyz789" Non -Matches : "123abc", "abc!", "Ab1"

Length

Static length string : is static and set when the string.

-Strings of Python. -String class : Java`s, C++, Ruby`s -Static length strings : C# and F# .

In Java : String strStatic = "Hello, World!";

Limited dynamic length string: is variable and set when the string

C and C++ .

In C , C++ : char myString[50];

Dynamic length string: is variable and not set when the string .

JavaScript and Perl.

In Perl : my $myString = "Hello, World!";

Primitive

Definition : Data types that are not defined in terms of other types .

Numeric Types

Most common primitive numeric data type

Java: Supports 4 signed integer types (byte, short, int, long) with different sizes and value ranges.

C++ and C# : supports unsigned integer types also .

Negative integers > are generally stored using two’s complement notation.

Some computers use one’s complement notation

Disadvantage:

By having two representations for zero:

Positive zero (all bits set to zero)

Negative zero (all bits set to one).

Floating-point

Floating-Point types are used to store real numbers, but the representations are only approximations for many real values .

Problem with floating-point types is the loss of accuracy through arithmetic operations .

On newer machines, floating-point numbers are represented using IEEE format.

Most languages include two floating-point types :

Float

Double

Precision is the accuracy of the fractional part of a value, measured as the number of bits.

Single Precision

Double Precision

Representation of the registering in the memory .

Range is a combination of the range of fractions and range of exponents.

Complex and Decimal Types

Some programming languages like Fortran and Python support .

Ex in Python: (7 + 5j) = imaginary par

Systems that support business applications provides hardware support for decimal types. , Ex : COBOL, C# and F# .

Advantage : The fractional parts can be stored precisely unlike floating-point types .

Disadvantage : Range of values for exponent are restricted .

Boolean Types

Simplest

Range include only two values : True and False.

ALGOL 60

C89 : Doesn`t have Boolean type = Numeric expressions as conditionals .

C99 and C+ : Provides Boolean type , Numeric expressions as conditionals .

Java and C# : Provides Boolean type , Doesn`t have Numeric expressions as conditionals .

Character Types

Character data are stored in computers as numeric coding.

Traditionally used coding was the 8-bit ASCII code. supports 128 different characters .

ISO 8859-1 : is another 8-bit character code which allows 256 different characters .

Ex : Ada 95+

In 1991 , UCS-2 standard ( Unicode ) : It is 16-bit character set

Java ( first language ) to support Unicode.

Ex : JavaScript, Python, Perl, C# and F# .

These points indicate how literal data is stored in computers and the evolution of encoding from ASCII to ISO 8859-1 to Unicode.

User-Defined Ordinal

Definition of ordinal types : is one in which the range of possible values can be easily associated with the set of positive integers.

Types

Enumeration

Is one in which all of the possible values (named constants) are provided in the definition.

Enumeration Constants : The named constants in an enumeration .

Starting Value

Implicit starting integer value for enumeration constants is 0.

Example of enumeration in C, C++ and C#

Design issues

Design issues: Whether an enumeration constant can appear in more than one type definition. Whether enumeration values are coerced to integers. Whether other types can be coerced to an enumeration type.

Subrange

Is a contiguous subsequence of an ordinal type.

- For example, 12..14 is a subrange of integer type. - Introduced by Pascal and are included in Ada.

Example in Ada

For example: - In lines 8-14: You can define a subrange type for weekdays based on the enumeration type Days. In this example, the subtype Weekdays represents a subrange of the Days enumeration type, specifically encompassing the weekdays from Monday to Friday. - In lines 16-23: The code demonstrates a subrange type for an index within the range of 1 to 100. In this case, the subtype Index represents a subrange of the Integer type, restricting the valid indexes to values between 1 and 100. it will output:

No existing languages other than Ada support subrange types.

Overall, enumeration types and subrange types provide ways to define specific subsets of values within larger ordinal types, allowing for more expressive and constrained data definitions.

By : Asmaa Alshamrani