complex data types -...

Complex Data Types

• Some languages support a complex type,

e.g., C99, Fortran, and Python

• Each value consists of two floats, the real

part and the imaginary part

• Literal form (in Python):

(7 + 3j), where 7 is the real part and 3 is

the imaginary part

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Primitive Data Types: Decimal

• For business applications

o Essential to COBOL

oC# offers a decimal data type

• Store a fixed number of decimal digits, in

coded form (BCD) - One byte per digit

• Advantage: accuracy

• Disadvantages: limited range, wastes

memory

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C# decimal type

• 128 bits = 16 byte representation

• Range: 1.0X10-28 to 7.9x1028

• Precision: exact to 28 or 29 decimal

places

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Primitive Data Types: Boolean

• Simplest of all

• Range of values: two elements, one for

“true” and one for “false”

• Could be implemented as bits, but is more

often implemented as bytes

o Advantage: readability

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Primitive Data Types: Character

• Stored as numeric coding

• Most commonly used coding: ASCII

• An alternative,16-bit coding: Unicode (UCS-2)

o Includes characters from most natural languages

o Originally used in Java

o C# and JavaScript also support Unicode

• 32-bit Unicode (UCS-4)

o Supported by Fortran, starting with 2003

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http://www.asciitable.com/

Character String Types

• Values are sequences of characters

• Design issues:

o Is it a primitive type or just a special kind of

array?

o Should the length of strings be static or

dynamic (determined at runtime)?

oWhat are the kinds of operations that you

would perform on a string?

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Character String Types Operations

• List the typical operations on Strings:

o Assignment and copying

oComparison (=, >, etc.)

oCatenation

o Substring reference

o Pattern matching

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String Type in Certain Languages

• C and C++ o Not primitive

o Use char arrays and a library of functions that provide operations

• SNOBOL4 (a string manipulation language) o Primitive

o Many operations, including elaborate pattern matching

• Fortran and Python (http://docs.python.org/library/string.html) o Primitive type with assignment and several operations

• Java o Primitive via the String class

• Perl, JavaScript, Ruby, and PHP o Provide built-in pattern matching, using regular expressions

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Character String Length Options

• Static: COBOL, Java’s String class

• Limited Dynamic Length: C and C++

o In these languages, a special character is

used to indicate the end of a string’s

characters, rather than maintaining the length

• Dynamic (no maximum): SNOBOL4, Perl,

JavaScript

• Ada supports all three string length options

o Static, Limited Dynamic and Dynamic

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Character String Type Evaluation

• Aid to writability

• As a primitive type with static length, they

are inexpensive to provide--why not have

them?

• Dynamic length is nice, but is it worth the

expense?

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Character String Implementation

• Static length: compile-time descriptor

• Limited dynamic length: may need a run-

time descriptor for length (but not in C and

C++)

• Dynamic length: need run-time descriptor;

allocation/de-allocation is the biggest

implementation problem

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Compile- and Run-Time Descriptors

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Compile-time descriptor for static strings

Run-time descriptor for limited dynamic strings

3-mins to discuss your string length type

Static, Limited Dynamic, Dynamic

• Static length strings are always full: if a

shorter string is assigned to a string variable,

the empty characters are set to blanks.

o Efficient but not very flexible and wasteful.

• Limited dynamic length - can store any

number of characters between zero and

the maximum, fast but not very flexible and

wasteful

• Dynamic length - slower but very flexible

and less wasteful

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User-Defined Ordinal Types

• An ordinal type is one in which the range

of possible values can be easily

associated with the set of positive integers

• Examples of primitive ordinal types in Java

o integer

o char

o boolean

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