Data Types I

Primitive data Types

•Almost all programming languages provide a set of primitive data types

•Primitive data types: Those not defined in terms of other data types

•Some primitive data types are merely reflections of the hardware

•Others require only a little non-hardware support for their implementation

Data types :

•Integer

•Floating Point

•Complex

•Decimal

•Boolean

•Character

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/deallocation is the biggest implementation

problem

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

–integer

–char

–boolean

Enumerated Type

•Aid to readability, e.g., no need to code a color as a number

•Aid to reliability, e.g., compiler can check:

–operations (don’t allow colors to be added)

–No enumeration variable can be assigned a value outside its defined range

–Ada, C#, and Java 5.0 provide better support for enumeration than C++ because enumeration type variables in these languages are not coerced into integer types

Subrange Type

•An ordered contiguous subsequence of an ordinal type

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

•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;

Array Types

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

•Indexing (or subscripting) is a mapping from indices to elements

   array_name (index_value_list) ®  an element

•Index Syntax

–Fortran and Ada use parentheses

•Ada explicitly uses parentheses to show uniformity between array references and function calls because both are mappings

–Most other languages use brackets

•FORTRAN, C: integer only

•Ada: integer or enumeration (includes Boolean and char)

•Java: integer types only

•Index range checking

  - C, C++, Perl, and Fortran do not specify

        range checking

    - Java, ML, C# specify range checking

    - In Ada, the default is to require range

        checking, but it can be turned off

Array Initialization

•Some language allow initialization at the time of storage allocation

–C, C++, Java, C# example

int list [] = {4, 5, 7, 83}

–Character strings in C and C++

char name [] = ″freddie″;

–Arrays of strings in C and C++

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

–Java initialization of String objects

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

Pointers in C and C++

•Extremely flexible but must be used with care

•Pointers can point at any variable regardless of when or where it was allocated

•Used for dynamic storage management and addressing

•Pointer arithmetic is possible

•Explicit dereferencing and address-of operators

•Domain type need not be fixed (void *)

   void *  can point to any type and can be type

      checked (cannot be de-referenced)

float stuff[100];

float *p;

p = stuff;

*(p+5) is equivalent to stuff[5] and  p[5]

*(p+i) is equivalent to stuff[i] and  p[i]

Reference

•Robert W. Sebesta - Concept of Programming Languages (Tenth Edition), Chapter 6