CSC204 Chapter 6: Data Types

Data Types

• A data type defines a collection of data values and a set of predefined operations on those values.
• A descriptor is the collection of the attributes of a variable.
• An object represents an instance of a user-defined (abstract data) type.

Primitive Data Types

• Primitive data types are not defined in terms of other data types.
• Examples of primitive data types include integers, floating-point numbers, and booleans.

Integer Data Type

• Integer is a primitive numeric data type.
• Java has four signed integer sizes: byte, short, int, and long.
• Negative integers can be stored in sign-magnitude notation or two's complement notation.

Floating-Point Data Type

• Floating-point values are represented as fractions and exponents, similar to scientific notation.
• Most languages support at least two floating-point types: float and double.
• Double variables usually occupy twice as much storage as float variables.

Boolean Data Type

• Boolean is the simplest of all types, with only two values: true and false.

Enumeration Types

• An enumeration type is a set of named constants.
• Example: enum days {mon, tue, wed, thu, fri, sat, sun};
• Enumeration types aid readability and reliability by preventing invalid values from being assigned.

Array Types

• An array is a homogeneous aggregate of data elements, where each element is identified by its position in the aggregate.
• The individual data elements of an array are of the same type.
• References to individual array elements are specified using subscript expressions.

Array Initialization

• Some languages allow initialization of arrays at the time of storage allocation.
• Examples: int list [] = {4, 5, 7, 83}; and char name [] = “freddie”;

Rectangular and Jagged Arrays

• A rectangular array is a multi-dimensional array where all rows have the same number of elements.
• A jagged array has rows with varying numbers of elements.
• C, C++, and Java support jagged arrays.

Associative Arrays

• An associative array is an unordered collection of data elements indexed by an equal number of values called keys.
• Example: %hi_temps = ("Mon" => 77, "Tue" => 79, "Wed" => 65, …);

Record Types

• A record is a heterogeneous aggregate of data elements, where individual elements are identified by names.
• Records are supported in C, C++, and C# using the struct data type.
• The fundamental difference between a record and an array is that record elements are not referenced by indices.

Pointer and Reference Types

• A pointer type variable has a range of values that consists of memory addresses and a special value, nil.
• Pointers provide the power of indirect addressing and a way to manage dynamic memory.
• Dereferencing yields the value stored at the location represented by the pointer’s value.

Type Checking and Strong Typing

• Type checking is the activity of ensuring that the operands of an operator are of compatible types.
• Strongly typed languages detect type errors at compile time or runtime.
• Examples: C and C++ are not strongly typed languages, while Java and C# are nearly strongly typed.