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Data Types, character string type, Specification of data type, how they…

- - - - allow us to implement "choice" into our algorithms
        
        represents the concepts of true and false
        
        simplest of all types
        
        more readable than other types such as integers
        
        common operations (algebra of Booleans) - and, or, not
        
        all languages recognize false as 0.
        
        some languages define true as -1 rather than 1.
        
        use single bit in the storage to store a boolean data value
        
        provision is made by languages for collection of bits
        
        used to control programming structures
    - - character set- the aggregate of characters that are used in a computer system or programming language
      - code points - numbers
      - code page- the assignments of numbers to characters in a set are collectively called
      - most commonly used coding
        
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        8-bit ASCII- uses 0..127 to code 128 different characters
        
        ISO 8859-1 - Allows 256 characters
      - collating sequence- the ordering of the characters in a character set - defines the ordering of characters for relational operations
      - python supports single characters only as character strings of length 1.
      - has a single character as its value
      - stored in computers as numeric codes
      - most programming languages include a primitive type for them
    - - Representation
        
        Computer
        
        supported by hardware
        
        as a group of binary digits (bits)
        
        Real world
        
        no fractional parts
        
        -basically, represents whole numbers
        
        Hardware Support
        
        others are supported by some programming languages, which are not directly supported by the hardware
        
        hardware of many computers supports several sizes of integers
        
        Difference between integer data types
        
        varies between language
        
        may or not be allowed to contain negative values
        
        unsigned types are used for binary data
        
        a signed integer value is represented in a computer by a string of bits, with one of the bits
        
        some languages include unsigned integer types, which are types for integer values without signs
        
        integer sizes available varies between machines
        
        operations on integer data
        
        Unary
        
        Relation
        
        Binary
        
        Arithmetic
        
        Bit
        
        Assignment
        
        Storage Representation
        
        sign-magnitude notation
        
        ones-complement notation
        
        an integer is represented by a string of bits
        
        convenient for addition and substraction
      - Floating Point Real Numbers
        
        computer representation
        
        two floating point types (float & double)
        
        float - standard size, stored in 4 bytes of memory
        
        double
        
        provided for larger fractional parts and/ or a larger range of exponents is needed
        
        occupy twice as much storage as float variables
        
        provide at least twice the number of bits of fraction
        
        a family of data types that act alike and differ only in the size of their domains
        
        precision- the accuracy of the fractional part of a value
        
        Range- combination of the range of fractions, range of exponents
        
        always are signed
        
        Representation
        
        real-world representation-real numbers
        
        computer world representation
        
        stored as mantissa and exponents
        
        IEEE Floating point standard 754 format
        
        data type
        
        called the floating point representation
        
        Single precision (32 bit) and double precision (64 bits) floating point variables
        
        represented as fractions and exponents
        
        issues
        
        Boolean operations are restricted
        
        some smaller computers do not have hardware support for floating point operations
        
        loss of accuracy
      - Decimal Type/ Fixed-point real numbers
        
        about
        
        primary data types for business data processing
        
        store a fixed number of decimal digits, with the decimal point at a fixed position in the value
        
        storage representation
        
        decimal point is not stored with the value
        
        data is stored as integers
        
        BCD-binary coded decimal
        
        scale factor - decimal point being an attribute of the data
        
        Advantages
        
        being able to precisely store decimal values, at least those within a restricted range
        
        Disadvantages
        
        no exponents are allowed
        
        representation in memory is mildly wasteful
        
        range of values is restricted
      - Complex Data Type
        
        Descriptors
        
        in an implementation, a descriptor is an area of memory that stores the attributes of a variable
        
        for dynamic attributes, the descriptor must be maintained during execution. in this case descriptor is used by the run time system,
        
        collection of the attributes of a variable
        
        used for type checking and building code for the allocation and deallocation operations
        
        1 more item...
        
        represented as ordered pairs of floating-point values
        
        some programming languages support a complex data type eg: Fortan & Python
        
        symbol table
        
        employed by the language translator
        
        information about
        
        declaration pr presence in the source code
        
        type
        
        scope level
  - - - Arrays may troublesome than primitive
        
        array requires loop for simple tasks
        
        implementing primitives is not easy
        
        implementation depends on language
  - - - used to assign names to integral constants
        
        the programmer defines
        
        literal names to be used for the values
        
        their ordering in a declaration
        
        an ordered list of distinct values
        
        the values in the definition become symbolic constants
        
        design issues
        
        are enumeration values coerced to integer?
        
        is a literal constant allowed to appear in more than one type definition
        
        Basic Operations
        
        assignment
        
        operations such as successor and predecessor
        
        relational operations
        
        used as loop variables or as array subscripts
        
        Advantages
        
        reliability
        
        readability
    - - contiguous subsequence of an ordinal type
      - All the operations defined for the parent type are also defined for the subrange
        type, except assignment of values outside the specified range.
      - in some languages subrange types are inbuilt to the language
      - C doesn't support subrange types
      - They define new names for possibly restricted or constrained versions of
        existing types.
      - implementation
        
        Range checking must be implicitly included by the compiler in every assignment of
        a variable or expression to a sub-range variable
        
        Usually implemented by associating a non-negative integer value with each
        symbolic constant in the type.
  - - - One-dimensional arrays - Vector
        
        Two-dimensional arrays - Matrix
        
        Multi-dimensional arrays
      - design issues
        
        when does array allocation take place?
        
        what types are legal for subscripts?
        
        number of array subscripts
        
        what is the lower bound of the subscript range and is it implicit?
      - Types of array data type
        
        four categories of arrays based on
        
        the binding to storage
        
        from where the storage is allocated
        
        the binding to subscript ranges
        
        Static Arrays
        
        storage allocation is static
        
        +efficiency- no dynamic allocation or deallocation is required
        
        subscript ranges are statically bound
        
        -size must be known at compile time
        
        Fixed Heap Dynamic Array
        
        storage bindings are doe when the user program requests them during execution
        
        storage is allocated from the heap, rather than the stack
        
        subscript ranges and the storage binding are both fixed after storage is allocated
        
        +flexibility- the array's size always fits the problem
        
        -allocation time from the heap, which is longer than allocation time from the stack
        
        Fixed Static -Dynamic Array
        
        +space efficiency; same memory locations can be used for other purposes
        
        -size must be known at compile time
        
        storage allocation is done at declaration elaboration time during execution
        
        -the required allocation and deallocation time
        
        subscript ranges are statically bound
        
        Heap-Dynamic Arrays
        
        binding of subscript ranges and storage allocation is dynamic in heap can change at any time during the array's lifetime.
        
        +flexibility- arrays can grow and shrink during program execution as the need for space changes
        
        -allocation and deallocation take longer and may happen many times during execution of the program
      - Initialization
        
        some languages provide the means to initialize arrays at the time their storage is allocated
      - Operations
        
        catenation
        
        comparison
        
        assignment
        
        equality inequality
      - 1D array data type
        
        single dimension array elements
        
        the code access array elements must be generated at compile time
        
        the descriptor stores information required to construct access information
      - 2D array data type
        
        two or more dimensions must be mapped onto a single dimensioned memory
        
        1 more item...
        
        hardware memory is linear
      - Multidimensional array data type
        
        rectangular array is a multidimensioned array (rectangular tables) in which all of the rows have the same number of elements and all of the
        columns have the same number of elements.
      - A jagged array is one in which the lengths of the rows need not be the
        same made possible when arrays are arrays of arrays.
      - Associative Arrays
        
        the user- defined keys must be stored in the
        structure. So each element is a key and a value.
  - - - basic elements of regulate expressions
        
        character sets
        
        quantifiers
        
        position indicators
    - - Generally, a regular expression engine stops the matching process
        after it detects the first match unless otherwise specified.
        
        Anchors : Meta characters that force the search to start relative to
        
        some specific point in the text string.
        
        ○ ^ - start of the string
        
        ○ $ - end of the
        
        ○ \Z - End of string
        
        ○ \b - Word boundary
        
        ○ \B - Not word boundary
        
        ○ \< - Start of word
        
        ○ > - End of word
- - - - allows to collect instances of entities
      - common attributes need not be considered
      - include only most significant attributes
      - view representation of an entity
  - - - can declare variables of that type, even though the actual representation is hidden from them
      - similar to process abstraction
      - includes the data representation of one specific data type
      - includes the subprograms that provide the options for that type
- - - - In COBOL computational variables
      - USAGE clause-specify the format of a data item/ variable in memory or in file record
      - In C register variables
  - - - storage representation such as bit representation, attribute representation, preferred location
      - static(dynamic) type checking
      - storage management-ex-size of the data block, allocation,lifetime
      - selection of correct operations if the operation is overloaded
- - - - programmer constructed
      - language provided
      - hardware provided-int
    - - Elementary data objects (primitive data types)
        
        values can be stored in fixed memory space
        
        all programming languages provide a set of primitive data types
        
        data types that are not defined in terms of other types
        
        ex: int, float, pointer, Boolean, char, double
        
        Data Structures (structured or non-scalar)
        
        building blocks of a structured type are its components
        
        aggregation of data object
        
        ex: arrays, records
        
        built out of other types
        
        require variable memory space to store the values
- - - - stores
        
        current length
        
        fixed max length
      - require more complex storage management
        
        pointer array
        
        faster than linked list
        
        extra memory
        
        linked list
        
        but simpler allocation and deallocation
        
        extra storage
        
        complex operations
        
        adjacent storage cells
        
        less storage required
        
        faster operations
        
        but not practical with increasing string size
      - require run time descriptor except in C & C++
    - - descriptor required only during compilation has
        
        name of type
        
        type length
        
        address of first character
    - - dynamic length strings