Org Ch6(Data Types)

What are the design issues for character string types?

-Is it a primitive type or just a special kind of array? - Should the length of strings be static or dynamic?

how many bits does it take to code a decimal digit

4 bits

What is a compatible type?

A compatible type is one that either is legal for the operator or is allowed under language rules to be implicitly converted by compiler-generated code to a legal type.

On what are Python's list comprehensions based?

A list comprehension is an idea derived from set notaion.

What is an aggregate constant?

A parenthesized lists of values.

Define strongly type.

A programming language is strongly typed if types errors are always detected.

What is the purpose of an F# tuple pattern?

A tuple pattern is simply a sequence of names, one for each element of the tuple , with or without the delimiting parentheses.

What arrays initialization feature is available in Ada that is not available in other common imperative languages?

Ada provides two mechanisms for initializing arrays in the declarations statements: by listing them in the order in which they are to be stored, or by directly assigning them to an index position using the => operator, which in Ada is called an arrow.

What are the advantages and disadvantages of decimal data types?

Advantage: accuracy Disadvantages: limited range, wastes memory

What is the structure of an associative array?

An associative array is an unordered collection of data elements that are indexed by an equal number of values called keys. User-defined keys must be stored.

Define ordinal, enumeration, and subrange types.

An ordinal type is one in which the range of possible values can be easily associated with the set of positive integers. An enumeration types is an all possible values, which are named constants, are provided in the definition. A subrange types is an ordered contiguous subsequence of an ordinal type.

In what ways are the user-defined enumeration types of C# more reliable than those of C++?

C# enumeration types are like those of C++, except that they are never coerced to integer. So, operations on enumeration types are restricted to those that make sense. Also, the range of values is restricted to that of the particular enumeration type.

What is a C++ reference type, and what is its common use?

C++ includes a special kind of pointer type called a reference type that is used primarily for formal parameters.

What is the purpose of level numbers in COBOL records?

COBOL uses level numbers to show nested records; others use recursive definition

What are the two common problems with pointers?

Dangling pointers (dangerous) and Lost heap-dynamic variable.

Define fully qualified and elliptical references to fields in records.

Fully qualified references must include all record names. Elliptical references allow leaving out record names as long as the reference is unambiguous.

How does JavaScript support sparse arrays?

Javascript objects are sparse, and arrays are just specialized objects with an auto-maintained length property (which is actually one larger than the largest index, not the number of defined elements) and some additional methods.

Are the unions of Ada always type checked?

No. the user can tell the system when the type checking can be static.

In what primarily imperative language do lists serve as arrays?

Python

Are the tuples of Python mutable?

Python includes an immutable tuple type

Describe the lazy and eager approaches to reclaiming garbage.

Reference counters (eager approach): reclamation is gradual. Mark-sweep (lazy approach): reclamation occurs when the list of variable space becomes empty.

What languages support array slices with stepsizes?

Ruby, Python, Perl.

What are the design issues for unions?

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

Describe the three string length options.

Static length: The length can be static and set when the string is created. compile-time descriptor Limited dynamic length: allow strings to have varying length up to a declared and fixed maximum set by the variable's definition. may need a run-time descriptor for length (but not in C and C++) Dynamic length: allow strings to have varying length with no maximum. need run-time descriptor; allocation/de-allocation is the biggest implementation problem

Define static, fixed stack-dynamic, stack-dynamic, fixed heap-dynamic, and heap dynamic arrays. What are the advantages of each?

Static: subscript ranges are statically bound and storage allocation is static (before run-time) Advantage: efficiency (no dynamic allocation). Fixed stack-dynamic: subscript ranges are statically bound, but the allocation is done at declaration time. Advantage: space efficiency . Stack-dynamic: subscript ranges are dynamically bound and the storage allocation is dynamic (done at run-time) Advantage: flexibility (the size of an array need not be known until the array is to be used). Fixed heap-dynamic: similar to fixed stack-dynamic: storage binding is dynamic but fixed after allocation (i.e., binding is done when requested and storage is allocated from heap, not stack). Heap-dynamic: binding of subscript ranges and storage allocation is dynamic and can change any number of times. Advantage: flexibility (arrays can grow or shrink during program execution).

What is the action of the Scheme function CAR?

The CAR function returns the first element of its list parameter.

What are the advantages of user-defined enumeration types?

The advantages are readability and reliability.

What are the design issues for pointer types?

What are the scope of and lifetime of a pointer variable? What is the lifetime of a heap-dynamic variable? Are pointers restricted as to the type of value to which they can point? Are pointers used for dynamic storage management, indirect addressing, or both? Should the language support pointer types, reference types, or both?

What are the design issues for arrays?

What types are legal for subscripts? Are subscripting expressions in element references range checked? When are subscript ranges bound? When does allocation take place? What is the maximum number of subscripts? Can array objects be initialized? Are any kind of slices supported?

what is a descriptor

a collection of the attributes of a variable

a length of a string can be varying in length up to a declared and fixed maximum set by the variables definition and called

a limited dynamic length strings

the length of a string can be static and set when the string is created and is called

a static length string

what is precision

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

character types used to be called ASCII, an 8 bit code but now

are represented by Unicode, a 16 bit character set

the most common string operations are

assignment, catentation, substring reference, comparison, and pattern matching

Why are reference variables in C++ better than pointers for formal parameters?

because a pointer refers to an address in memory while a reference refers to an object or a value in memory.

Why is Java not strongly typed?

because there are no implicit ways type errors can go undetected.

java includes 4 signed integer sizes

byte, short, int, long

C and C++ use char arrays to store

character strings

character types in python are actually

character strings of length 1

enumeration types provide a way of defining and grouping

collections of named constants , which are called enumeration constants

special hardware support is required for

decimal data types

what is a data type

defines a collection of data objects and a set of predefined operations on those objects

the two user defined ordinal types are

enumeration and subrange

boolean types are often used to represent

flags or switches

two common floating point types are called

float and double

character string literals that are built by the compiler also

have the null character to indicate the array has terminated

What happens when a nonexistent element of an array is referenced in Perl?

if you try to append non-existent elements from an array to another one, the initial array will grow as needed, even though the elements to append do not exist.

enumeration constants are typically

implicitly assigned the integer values 0,1,...but can be explicitly assigned any integer literal in the types definition

an enumeration type is one in which all the possible values which are named constants are provided or enumerated

in the definition

what is the most common primitive numeric data type is

integer

in java the primitive ordinal types are

integer, char and boolean

the first field of every static descriptor

is the name of the type

the second field of every static descriptor

is the second field is the type's length(in characters)

What is the action of the F# fuction tl?

it is the methods of the List class, as in List.hd[1; 3; 5; 7], which returns 1

booleans are typically stored in a byte because

it is usually the smallest efficiently addressable cell of memory

an ordinal type is

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

the string manipulation functions of the C standard library are also available in C++, and are inherently unsafe because they dont guarantee against overflow and so

programmers in C++ should use the string class from the std library rather than char arrays from the C library

the collection of values that can be represented by a floating point type is defined by

range and precision

what is range

range is combination of the range of fractions, and the range of exponents

floating point data types model

real numbers *but the representations are only approximations for many real values

What is the primary difference between a record and a tuple?

record is an aggregate of data elements in which the individual elements are identified by names and accessed through offsets from the beginning of the structure. tuple is a data type that is similar to a record, except that the elements are not named.

how are complex numbers represented in Fortan and Python

represented as ordered pairs of floating point values

static length and limited dynamic length strings

require no special dynamic storage allocation

a character string type are types where the values consist of

sequences of characters

substring references are often called

slices

character strings can be supported directly in hardware but

software usually is used to implement storage, retrieval and manipulation

dynamic length strings require more complex

storage management

run time descriptor for limited dynamic strings require only

storing both the fixed maximum length and the current length

what are the three approaches to supporting the dynamic allocation and deallocation that is required for dynamic length strings

strings can be stored in a linked list strings can be stored as an array of pointers to individual characters allocated in the heap store complete strings in adjacent storage cells

if strings are not defined as a primitive type

strings data is usually stored in arrays of single characters and referenced this way

strings from the String class are immutable but

strings from the StringBuffer class is mutable , more like arrays of singel characters

a subrange type is a contiguous

subsequence of an ordinal type *for example, 12...14 is a subrange of an integer type

the third field of every static descriptor

the address of the first character

What advantages do Java and C# reference type variables have over the pointers in other languages?

the reference Java and C# provide some of the flexibility and the capabilities of pointers, without the hazards.

a length of a string can also be a varying length with no maximum in some languages, such as JS, Perl and C++ and

these are called dynamic length strings

the double type is provided when needed for larger range and usually store

twice as many number of bits

Define type error.

type error is the application of an operator to an operand of an inappropriate type.

Define union, free union, and discriminated union.

union: a type whose variables are allowed to store different type values at different times during execution. free union: provide union constructs in which there is no language support for type checking. Discriminated union: type checking of unions require that each union include a type indicator.

decimal types are stored like character strings

using binary codes for decimal digits (BCD)

the float type is the standard size

usually stored in four bytes of memory

What is nonconverting cast?

when no conversion takes place. It is merely a means of extracting the value of a variable of one type and using it as if it were of a different type.

a descriptor for a static character string type

which is required only during compilation has three fields

most computers store floating points in binary

which only makes approximations worse *0.1 cannot be represented in binary by a finite number of binary digits

Are the unions of F# discriminated?

yes.