cosc237/structures1 Structures aggregate data types record - single variable name for the whole collection composed of several variables - fields,BUT, unlike arrays, members also have names - field names, and may be different types; member

cosc237/structures2 Declaration 1. define template - form of the structure; struct name (or tag) { type member1; type member2; … };// no space reserved 2. Declare structure variable structname varname;/* allocates space */

cosc237/structures3 Example: struct Employee// structure tag { int idNumber; char name[30]; float salary; }; essentially creates a new variable type Employee emp1; Employee newEmp;

cosc237/structures4 Struct cont’d size determined by sum of all individual members ; required,tag is optional - anonymous struct { int idNumber; char name[30]; float salary; } newEmp;

cosc237/structures5 struct AnimalType // declares a struct data type, does not allocate memory { // struct members long id; char name[20]; char genus[10]; char species[10]; char country[15]; int age; float weight; }; // declare variables of AnimalType AnimalType animal1; AnimalType animal2;

cosc237/structures6 templates struct point { int x; //x-coordinate int y; //y-coordinate }; { int idNumber; char LName[30]; char FName[15]; float salary; };

cosc237/structures7 Scope of member name Member name is local to struct struct Employee// structure tag { int idNumber; char name[30]; float salary; }; struct Student { char ssNum[9]; char name[30]; }

cosc237/structures8 Declaration for structure variables: allocates space Example: 1. point point1; 2. Employee emp1; Employee emp2;

cosc237/structures9 Accessing individual members dot (.) operator is the member selection operator. structureName.memberName memberName not unique it is possible for members of different struct types to have the same identifiers. Also a non-struct variable may have the same identifier as a structure member. Examples: thisAnimal.weight, point1.x, point1.y, point2.x, point2.y; emp1.idNumber = 111; emp2.salary = 42000;

cosc237/structures10 Initialization structure variables can be initialized when they are declared: Employee newEmp = {999, "Ford", "John", 50000}; point point1 = {5, 10}; //x = 5 y = 10

cosc237/structures11 Reference animal1.age = 18; animal1.age++; animal2.id = ; cin >> animal1.weight; animal2.name = "giant panda"; animal2.genus[0] = toupper(animal2.genus[0]); newEmp.salary = newEmp.salary ; sizeof newEmp or sizeof (Employee)

cosc237/structures12 Strings in structures newEmp.name - “George” newEmp.name[0] - ‘G’ newEmp.name[1] - ‘e’

cosc237/structures13 Assignment one struct variable can be assigned to another, if both variables are of the same type –Employee emp1,emp2; –emp1 = emp2; Type compatibility - only if their types are identical or are renamings of the same type typedef Employee Worker;

cosc237/structures14 Operations valid on an entire struct type variable: Assignment operation: one struct variable can be assigned to another struct variable if both variables are of the same type. Example: –Employee emp1, emp2; emp1 = emp2; //copies the entire structure, member by member

cosc237/structures15 Telling Functions about Structures Structures can be passed as function arguments and can be returned as function return values. It's wasteful to pass large structures to a function that uses only one or two members of the structure. Can be passed by value or ref using same method as int, float, etc.

cosc237/structures16 Invalid Structure Operations (i.e.structure as a whole unit) I/O: cannot print or input structures as a whole cout >> newEmp;// invalid cout >> emp1.idNumber; Comparison: cannot compare entire structures if (emp1 < emp2) // invalid if (emp1.idNumber < emp2.idNumber)… // valid Arithmetic: cannot do arithmetic on entire structures newEmp = emp1 + emp2; // invalid newEmp.salary = emp1.salary + emp2.salary;// valid

cosc237/structures17 Examples of valid operations animal1 = animal2; // assignment, same type WriteOut(animal2); // value parameter ChangeAge(animal2); // reference parameter animal1 = GetAnimalData( ); // return value of function void ChangeAge ( AnimalType& thisAnimal) // struct as function argument { thisAnimal.age++; } AnimalType GetAnimalData ( ) // struct returned as function return value // Obtains all information about an animal from keyboard { AnimalType thisAnimal; char response; do { // have user enter all members until they are correct... } while (response != 'Y' ); return thisAnimal; }

cosc237/structures18 Hierarchical or nested structures struct DateType { int month; // Assume int day; // Assume int year; // Assume }; struct StatisticsType { float failRate; DateType lastServiced; // DateType is a struct type int downDays; }; struct MachineRec { int idNumber; char description[30]; StatisticsType history; // StatisticsType is a struct type DateType purchaseDate; // DateType is a struct type float cost; }; MachineRec machine; //variable of type MachineRec cout << machine.history.lastServiced.year; // may be 2001

cosc237/structures19 Example struct point { int x; //x-coordinate int y; //y-coordinate }; struct line { point start; // start point point end; // end point }; line diagonal; // variable of type line cout << diagonal.start.x; //the x-coord of the start point

cosc237/structures20 In general, structs are worthwhile only when used in combination with arrays (and, in later chapters, with pointers). Arrays and structs may be combined in various ways to form complex data structures. We can have arrays of structs, structs that contain arrays, arrays of structs with array components, and so on.

cosc237/structures21 Array of Structures Declaration const int NUM_COMP_EMP = 20; Employee compDept[NUM_COMP_EMP]; reference: arrayName[index].someMember compDept[0].name compDept[1].idNnumber not compDept.salary[0] compDept[2].name[3]

cosc237/structures22 Example struct point { int x; //x-coordinate int y; //y-coordinate }; point points[10]; //array variable of type point

cosc237/structures23 Example /* print the names of the employees in the computer department */ for (i = 0; i < NUM_COMP_EMP; i++) cout << compDept[i].name << endl;

cosc237/structures24 Unions device that lets you store different data types in the same memory space when several variables of different names refer to the same storage space; compiler reserves memory large enough to hold the largest data type

cosc237/structures25 Declaration: (similar to structures) union MixedArray { char name[10]; int age; float salary; double census; }; Define union variables: MixedArray p0; MixedArray save[10];

cosc237/structures26 Exa. union Holdem { int digit; double bigfl; char letter; } fit; fit - sizeof double fit.digit = 23;/* 23 is stored in fit,4 bytes used */ fit.bigfl = 2.0;/* 23 cleared, 2.0 stored; 8 bytes used fit.letter = 'h'; /* 2.0 cleared, h stored, 1 byte used */

cosc237/structures27 Anonymous Unions union { int someInt; float someFloat; }; member names are not local to union dot notation not used someInt = 67; used with Variant Records

cosc237/structures28 Variant Records Struct consisting of type field and one or more anonymous unions the member the anonymous union is called variant avoid nesting variant records within variant records always use a type field