Structure

Structure

• 1.
  1 Records C++ Structs Chapter 14
• 2.
  2 What to dowith records? Declaring records Accessing records Accessing the field of a record What is a union? Can records be in arrays?
• 3.
  3 Records Recall that elementsof arrays must all be of the same type In some situations, we wish to group elements of different types scores : 85 79 92 57 68 80 . . . 0 1 2 3 4 5 98 99 employee R. Jones 123 Elm 6/12/55 $14.75
• 4.
  4 Records RECORDS are usedto group related components of different types Components of the record are called fields In C++ – record called a struct (structure) – fields called members employee R. Jones 123 Elm 6/12/55 $14.75
• 5.
  5 Records C++ struct – structureddata type – fixed number of components – elements accessed by name, not by index – components may be of different types struct part_struct { char descrip [31], part_num [11]; float unit_price; int qty; };
• 6.
  6 Declaring struct Variables Given Declare: struct part_struct { char descrip [31], part_num [11]; float unit_price; int qty; }; part_struct new_part, old_part; Use struct name as a type.
• 7.
  7 Accessing Components Use thename of the record the name of the member separated by a dot . The dot is called the member selector old_part.qty = 5; cout << new_part.descrip;
• 8.
  8 Aggregate Operations with Structures Recallthat arrays had none (except reference parameter) Structures DO have aggregate operators – assignment statement = – parameter (value or reference) – return a structure as a function type
• 9.
  9 Aggregate Operations with Structures Limitationson aggregate operations – no I/O – no arithmetic operations – no comparisons cout << old_part; cin >> new_part; old_part = new_part + old_part; if (old_part < new_part) cout << ...;
• 10.
  10 Aggregate Operations with Structures struct variables must be compared member-wise.  To compare the values of student and newStudent, you must compare them member-wise, as follows: if(student.firstName == newStudent.firstName && student.lastName == newStudent.lastName) ...
• 11.
  11 Input/Output  There areno aggregate input/output operations on struct. • Data in a struct variable must be read one member at a time. • Contents of a struct must be written one member at a time.
• 12.
  12 struct Variables andFunctions  A struct variable can be passed as a parameter either by value or by reference. A function can return a value of the type struct Note example program fragment
• 13.
  13 Contrast Arrays andstructs
• 14.
  14 Arrays of Records Firstdeclare a struct (such as part_struct) Then specify an array of that type Access elements of the array, elements of the struct part_struct part_list [50]; for (x = 0; x <50; x++) cout << _______________________; How do we print all the descrip fields? part_list[x].descrip
• 15.
  15 Records with Arrays Example constarraySize = 1000; struct listType { int elements[arraySize]; //array containing the list int listLength; //length of the list } See sample program
• 16.
  16 Hierarchical Records Defn =>records where at least one of the components is, itself, a record Example: struct inventory_struct { part_struct part; int qty_sold, re_order_qty; vendor_struct vendor; };
• 17.
  17 Unions defn => astruct that holds only one of its members at a time during program execution union Qty_type { int count; float linear_ft; long cu_in; }; Qty_type how_many; At run time, how_many contains either •an int •a float •a long . . . But … never all three
• 18.
  18 Choosing Data Structures Striveto group logical elements of a structure together – calls for hierarchical structures Push details of entities down to lower levels of the structure Data Abstraction <=> separation of logical peoperties of a data type from its implementation
• 19.
  19 Testing and DebuggingHints Declaration of a struct type must end with a semicolon ; Be sure to specify the full member selector when referencing a component of a struct variable – don’t leave out the struct name
• 20.
  20 Testing and Debugging Whenusing an array in a struct, the index goes at the end student_rec.scores[x] When using an array of struct, the index goes after the struct name parts_list[x].qty
• 21.
  21 Testing and Debugging Processstruct members separately … the only aggregate operations will be Assignment = Parameter passing void do_it (part_struct part); Function return part_struct blanked_part ( );
• 22.
  22 Testing and Debugging Becareful using same member names in different struct types Compiler keeps them separate OK Human readers can easily confuse them struct parts { int qty; . . . } ; struct test_scores { int qty; . . . } ;