Simple vs Structured Data

Transcription

1 Simple vs Structured Data Scalar Data Types - int, float An atomic data item One memory location for a symbolic name Cannot be decomposed Structured Data Types - arrays, structs, union, class A collection of components, data items, with an imposed organization Entire collection is given a single name Each component is accessed individually C++ Data Types / \ / \ / \ simple char, int, float structured / \ / \ / \ array struct union class 1

2 Structs (Record) Block of memory locations (fields) given one name Heterogeneous - fields can be different data types Each component, field, is called a member A member name is given to each field for accessing struct StructName optional { DataType MemberName; MemberList DataType MemberName; } Variables optional ;... Example: struct ItemRecType // Type declaration { int qty; float cost; bool taxable; } item1; // Variable declaration ItemRecType item2; //Variable declaration Without the Type name variables are of anonymous type, no other variables can be declared with the same type. Without the variable declarations it is a type declaration only Access A member is accessed by the member s name and the member selector (dot). StructVariable.MemberName; Example: item1.cost = 57.98; Aggregate Operations Assignment is permitted - two struct variables of the same type can be assigned to each other. Copies the contents of the struct variable to the other struct variable, member by member. Example: item2 = item1; // Assigns all field values in item1 to item2 2

3 Passing Struct as Parameters Can be call by value or call by reference Can be a return value of a function Examples: SomeFunction(item1) // Valid call void SomeFunction(itemRecType item) void SomeFunction(itemrecType & item) item1 = SomeFunction2( ); itemrectype SomeFunction2( ); // function header - pass by value // function header - pass by reference // Valid call // function header showing ret type Hierarchical Records - Records in which at least one of the components is a record. struct DateType { int month; int day; int year; }; enum Gradetype {A, B, C, D, F}; struct StudentRec { string first; string last; DateType birthday; // uses record as datatype float gpa; int programs; int quizzes; int final; GradeType grade; // uses enum as datatype }; StudentRec s1, s2; s1.grade = C; s2.birthday.month = 10; 3

4 Unions A structure that holds only one of its members at a time during program execution. Purpose is to conserve memory by forcing several members to use the same memory space. Example: union bytetype { long bytes; int KB; float MB; float GB; }; bytetype disk1; disk1.bytes = ; disk1.kb = 23; // replaces the disk1.mb = 1.44; // replaces the 23 Example 2: enum DiskType {SM_FLOPPY, LG_FLOPPY}; struct DiskRec { DiskType kind; ByteType size; } DiskRec floppy; if (floppy.kind == SM_FLOPPY) //3.5in floppy.size.mb = 1.44; else floppy.size.kb = 720; 4

5 User-Written Header files create your own header files in your directory need to use the preprocessor directive to include in your program: #include filename.h ex: #include item.h // data type def. need to be sure that no multiple inclusion of head files. Surround all code in the head file with: #ifndef _SOMEIDENTIFIER #define _SOMEIDENTIFIER. header file contents #endif 5

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