Programmer Defined Structures (Records)

1. Programmer Defined Structures (Records) CS362

2. C++ Structures • A Structure (Record) Contains Data About a Single Entity: • Each Data Item is Called a Member (or Field) • Members Can Be Of Different Data Types • Member Data Types Can Be Basic or Complex • Basic – int, float, double, string • Complex – array, other structures • In The End, Any Valid Data Type Can Used to Define a Member in a Structure

3. C++ Structures • Data About a Student May Consist of: • Last Name string • First Name string • Middle Initial char • Id Number int • Sex char • GPA float • Putting This All Together We Can Define A Structure

4. Defining A Structure • Structures Require a Two Step Definition Process: • First – Define a struct Data Type That Defines the Members of the Required Structure • Second – Use the struct to Declare Variables Needed for the Program • struct Data Type Definition: struct struct-name { type member1-name; type member2-name; : type memberN-name; };

5. Defining A Structure • Definition Rules: • The Structure Definition Must Begin With Reserved Word – struct • Each Member Must Have a Type (the Type Can Be Different Then Other Members) • Semicolons Separate the Structure Members • Structure Definition Must End With };

6. Defining A Structure Variable • The struct Definition Only Defines a Data Type • To Use the Structure, Memory Must be Allocated Via Variable Declaration: struct-type variable_identifier; • Where struct-type is the Structure Type Declared • Where variable identifier is a Valid Identifier Name

7. Initializing A Structure Variable • Like Other Variables Structures Can be Initialized at Declaration: struct-type variable_identifier = {member1-value, member2-value, ….memberN-value};

8. Structure Example struct studentRec { int idNumber; string lname; string fname; char initial; char sex; double gpa; };

9. Structure Variable studentRec stu1; stu1 Initialized studentRec stu1 = {123456,”Sanders”,”Mark”,’S’,’M’,3.50}; stu1

10. Accessing Structure Data • A Structure is a Single Data Unit • Members Can Be Accessed Individually • To Access a Member Use The DOT notation: structvariable_name.member_name studentRec.lname = “Sanders”; • Members Can Be Used Like Any Other Variable

11. Accessing Structure Data (cont.) • More Examples cout << “Enter student GPA: “; cin >> stu1.gpa; stu1.gpa = stu1.gpa + 0.5; cout << fixed << showpoint << setprecision(2); cout << stu1.lname << “, “ << stu1.fname << “ “ <<; cout << stu1.gpa << endl;

12. Using Structure Data • Once You Have Data in the Structure, it Can Be Used Like Any Other Variable: if (stu1.sex == ‘F’) { cout << stu1.fname << ‘ ’ << stu1.lname << “ is Female.”; cout << endl; } if (stu1.gpa < 2.5) { cout << stu1.lname << “, ” << stu1.fname; cout << “ is on probation.” << endl; }

13. Structures As Arguments • Structures Can Be Passed as Data to Functions • If Data is to be Modified, Pass By Reference void readStuInfo (studentRec& stu1) { cout << “Enter student last name: “; cin >> stu1.lname; : cout << “Enter student GPA: “; cin >> stu1.gpa; }

14. Arrays of Structures • Rather Than Using Parallel Arrays, we can use an Array of Structures • Does Not Violate Single Data Type Rule • Each Cell In The Array Will Hold One Structure struct-type array_name[size]; studentRecstudentList[MAX]; • Declares Array to Store MAX Quantity of Structures • Each Cell Contains One Record With Six Members

15. Initializing Structure Array • Same As In The Past, Only Thing New Is the Subscript studentRec studentList[MAX] = { {123456,”Sanders”, “Mark”, ‘S’, ‘M’, 3.50}, {234789, “Blow”, “Joe”, ‘J’,‘M’, 2.50}, {367890, “Smith”, “Sally”, ‘S’,‘F’, 4.00} }; • All Remaining Cells Are Initialized to “blank” or 0

16. Accessing Structure Array Data • Just Need To Use Subscript: arrayName[index].member_name studentList[1].idNumber = 234567; studentList[2].gpa = studentList[3].gpa; for (num = 0; num < MAX; num++) { cout << studentList[num].lname << “, ” <<; cout << studentList[num].fname << endl; }

17. Access Structure Array Data (cont.) • Swapping Structures is like Swapping Any Variables: studentRec temp; temp = studentList[top]; studentList[top] = studentList[minPosition]; studentList[minPosition] = temp;

18. Nested Structure • A Nested Structure is a Structure that has a Member that is a Structure • Used to Organize Data, and to Allow for the Reuse of Variable Names • To Declare a Nested Structure You Must First Declare the Structure(s) that will be Nested • Once Declared the Structure can be used as Data Type for Members of Other Structures

19. Nested Structure (cont.) struct address { string street; string city; string state; string zip; }; struct student { string lname; string fname; int age; double gpa; address campus; address home; }; student studentData;

20. Nested Structure (cont.) • Accessing Nested Structure • Need to Use Entire Name: studentData.lname studentData.fname studentData.age studentData.gpa studentData.campus.street studentData.campus.city studentData.campus.state studentData.campus.zip studentData.home.street studentData.home.city studentData.home.state studentData.home.zip

21. Nested Structure (cont.) • Arrays of Nested Structures student studentList[MAX]; studentList[n].lname studentList[n].fname studentList[n].age studentList[n].gpa studentList[n].campus.street “ “ “ “ “ “ studentList[n].campus.zip studentList[n].home.street “ “ “ “ “ “ studentList[n].home.zip