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CHAPTER 12 RECORDS ( Struct s)

CHAPTER 12 RECORDS ( Struct s). In this chapter, you will: Learn about records ( struct s) Examine various operations on a struct Explore ways to manipulate data using a struct Learn about the relationship between a struct and functions Discover how arrays are used in a struct

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CHAPTER 12 RECORDS ( Struct s)

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  1. CHAPTER 12RECORDS (Structs)

  2. In this chapter, you will: • Learn about records (structs) • Examine various operations on a struct • Explore ways to manipulate data using a struct • Learn about the relationship between a struct and functions • Discover how arrays are used in a struct • Learn how to create an array of struct items

  3. Records (Struct) • struct: A collection of fixed number of components in which components are accessed by name is called a struct. The components may be of different types. • The components of a struct are called the members of the struct. • The general form (syntax) of a structin C++ is: struct typeName { dataType1 identifier1; dataType2 identifier2; . . . dataTypen identifiern; };

  4. In C++, structis a reserved word. • A semicolon at the end of astructdefinition is a part of the syntax.

  5. struct employeeType { string firstName; string lastName; string address1; string address2; double salary; string deptID; }; • struct is a definition not a declaration. No memory is allocated. • Memory is allocated when we declare variables.

  6. struct studentType { string firstName; string lastName; char courseGrade; int testScore; int programmingScore; double GPA; }; //variable declaration studentType newStudent; studentType student;

  7. Accessing structMembers • The syntax for accessing astructmember is: structVariableName.MemberName • In C++, the . (dot) is an operator, called the member access operator.

  8. newstudent.gpa = 0.0; newStudent.firstName = "John"; newStudent.lastName = "Brown";

  9. The statement cin>>newstudent.firstName; reads the next string from the standard input device and stores it in newstudent.firstName. • The statement cin>>newstudent.testScore>>newstudent.programmingScore; reads two integer values from the keyboard and stores them in newStudent.testScore and newStudent.programmingScore, respectively. score = newStudent.testScore + newStudent.programmingScore;

  10. if(score >= 90) newStudent.courseGrade = 'A'; else if(score >= 80) newStudent.courseGrade = 'B'; else if(score >= 70) newStudent.courseGrade = 'C'; else if(score >= 60) newStudent.courseGrade = 'D'; else newStudent.courseGrade = 'F';

  11. Assignment We can assign the value of one struct variable to another struct variable of the same type using an assignment statement.

  12. student = newstudent;

  13. student = newstudent; This statement is equivalent to the following statements: student.firstName = newStudent.firstName; student.lastName = newStudent.lastName; student.courseGrade = newStudent.courseGrade; student.testScore = newStudent.testScore; student.programmingScore = newStudent.programmingScore; student.GPA = newStudent.GPA;

  14. Comparison • 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) . . .

  15. Input/Output • There are no 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. The statement cout<<newStudent.firstName<<" " <<newStudent.lastName<<" " <<newStudent.courseGrade<<" " <<newStudent.testScore<<" " <<newStudent.programmingScore<<" " <<newStudent.GPA<<endl; outputs the content of the struct variable newstudent.

  16. struct Variables and Functions • 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.

  17. void readIn(studentType& student) { int score; cin>>student.firstName>>student.lastName; cin>>student.testScore>>student.programmingScore; cin>>student.GPA; score = newStudent.testScore + newStudent.programmingScore; if(score >= 90) student.courseGrade = 'A'; else if(score >= 80) student.courseGrade = 'B'; else if(score >= 70) student.courseGrade = 'C'; else if(score >= 60) student.courseGrade = 'D'; else student.courseGrade = 'F'; }

  18. The statement readIn(newStudent); calls the function readIn. • The function readIn stores the appropriate information in the variable newStudent.

  19. void printStudent(studentType student) { cout<<student.firstName<<" " <<student.lastName<<" " <<student.courseGrade<<" " <<student.testScore<<" " <<student.programmingScore<<" " <<student.GPA<<endl; }

  20. Arrays in Structs • The two things that are associated with a list are the values (that is, elements) and the length of the list. • In the searching and sorting functions that we discussed, we needed to pass these two things separately to the function. • The values and the length are both related to a list we can define a struct containing both the items. • We need to pass only one parameter not two.

  21. const arraySize = 1000; struct listType { int elements[arraySize]; //array containing the list int listLength; //length of the list }

  22. int seqSearch(const listType& list, int searchItem) { int loc; boolfound = false; for(loc = 0; loc < list.listLength; loc++) if(list.elements[loc] == searchItem) { found = true; break; } if(found) return loc; else return –1; }

  23. Structs in Arrays • Suppose there are 50 full time employees in a company. • Print their monthly pay check and also keep track of how much money has been paid year to date. • Define an employee’s record. struct employeeType { string firstName; string lastName; int personID; string deptID; double yearlySalary; double monthlySalary double yearToDatePaid; double monthlyBonus; };

  24. employeeType employees[50];

  25. The following C++ code loads the data into the employees’ array. • We assume that initially yearToDatePaid is 0 and that the monthly bonus is determined each month based on performance. ifstream infile; //input stream variable assume //that employee.dat file has been opened for(counter = 0; counter < 50; counter++) { infile>>employees[counter].firstName >>employees[counter].lastName >>employees[counter].SSN >>employees[counter].deptID >>employees[counter].yearlySalary; employees[counter].monthlySalary = employees[counter].yearlySalary/12; employees[counter].yearToDatePaid = 0.0; employees[counter].monthlyBonus = 0.0; }

  26. double payCheck;//variable to calculate the paycheck for(counter = 0; counter < 50; counter++) { cout<<employees[counter].firstName<<" " <<employees[counter].lastName<<" "; payCheck = employees[counter].monthlySalary + employees[counter].monthlyBonus; employees[counter].yearToDatePaid = employees[counter].yearToDatePaid + payCheck; cout<<setprecision(2)<<payCheck<<endl; }

  27. Structs within a struct Let us consider the following record of an employee: struct employeeType { string firstname; string middlename; string lastname; string emplID; string address1; string address2; string city; string state; string zip; string hiremonth; string hireday; string hireyear;

  28. string quitmonth; string quitday; string quityear; string phone; string cellphone; string fax; string pager; string email; string deptID; double salary; };

  29. struct nameType { string firstname; string middlename; string lastname; }; struct addressType { string address1; string address2; string city; string state; string zip; };

  30. struct dateType { string month; string day; string year; }; struct contactType { string phone; string cellphone; string fax; string pager; string email; };

  31. struct employeeType { nameType name; string emplID; addressType address; dateType hiredate; dateType quitdate; contactType contact; string deptID; double salary; }; // variable declaration employeeType newEmployee; employeeType employees[100];

  32. newEmployee.salary = 45678.00; newEmployee.name.first = "Mary"; newEmployee.name.middle = "Beth"; newEmployee.name.last = "Simmons"; cin>>newEmployee.name.first; newEmployee.salary = newEmployee.salary * 1.05; for(j = 0; j < 100; j++) cin>>employees[j].name.first >>employees[j].name.middle >>employees[j].name.last;

  33. PROGRAMMING EXAMPLE: SALES DATA ANALYSIS A company has six salespeople. Every month they go on road trips to sell the company’s product. At the end of each month, the total sales for each salesperson, together with that salesperson’s ID and the month, is recorded in a file. At the end of each year, the manager of the company wants to see the report in the following tabular format:

  34. ----------- Annual Sales Report ------------- ID QT1 QT2 QT3 QT4 Total _______________________________________________________________ 12345 1892.00 0.00 494.00 322.00 2708.00 32214 343.00 892.00 9023.00 0.00 10258.00 23422 1395.00 1901.00 0.00 0.00 3296.00 57373 893.00 892.00 8834.00 0.00 10619.00 35864 2882.00 1221.00 0.00 1223.00 5326.00 54654 893.00 0.00 392.00 3420.00 4705.00 Total 8298.00 4906.00 18743.00 4965.00 Max Sale by SalesPerson: ID = 57373, Amount = $10619.00 Max Sale by Quarter: Quarter = 3, Amount = $18743.00 QT1 stands for quarter 1 (months 1 to 3), QT2 for quarter 2 (months 4 to 6), QT3 for quarter 3 (months 7 to 9) and QT4 for quarter 4 (months 10 to 12).

  35. The salespeople’s IDs are stored in one file; sales data are stored in another file. The sales data is in the following form: salesPersonID month saleAmount . . . • The sales data is in no particular order; it is not ordered by ID. Input: One file containing each salesperson’s ID, and a second file containing the sales data. Output: A file containing annual sales report in the above format.

  36. Problem Analysis and Algorithm Design struct salesPersonRec { string ID; //salesperson’s ID double saleByQuarter[4]; //array to store the total //sales for each quarter double totalSale; //salesperson’s yearly //sales amount }; salesPersonRec salesPersonList[noOfSalesPersons]; double totalSaleByQuarter[4];

  37. Read the salespeople’s IDs into the array salesPersonList and initialize the quarterly sales and total sales for each salesperson to 0.

  38. For each entry in the file containing the sales data, 1. Read the salesperson’s ID, month, and sale amount for the month. 2. Search the array salesPersonList to locate the component corresponding to this salesperson. 3. Determine the quarter corresponding to the month. 4. Update the sales for the quarter by adding the sale amount for the month. Once the sales data file is processed a. Calculate the total sale by salesman. b. Calculate the total sale by quarter. c. Print the report.

  39. The above discussion translates into the following algorithm. 1. Initialize the array sales. 2. Process the sales data. 3. Calculate the total sale by salesman. 4. Calculate the total sale by quarter. 5. Print the report. 6. Calculate and print the maximum sale by salesman. 7. Calculate and print the maximum sale by quarter.

  40. Function initialize void initialize(ifstream& indata, salesPersonRec list[], int listSize) { int count; quarterType quarter; for(count = 0; count < listSize; count++) { indata>>list[count].ID; //get salesperson’s ID for(quarter = QT1; quarter <= QT4; quarter = static_cast<quarterType>(quarter + 1)) list[count].saleByQuarter[quarter] = 0.0; list[count].totalSale = 0.0; } }

  41. Function getData: 1. Read the salesperson’s ID, month, and sales amount for the month. 2. Search the array salesPersonList to locate the component corresponding to the salesperson. (Because the salespeople’s IDs are not sorted, we will use a sequential search to search the array.) 3. Determine the quarter corresponding to the month. 4. Update the sales for the quarter by adding the sales amount for the month. Suppose that the entry read is: 57373 2 350 Here the salesperson’s ID is 57373, the month is 2, and sale amount is 350.

  42. After processing this entry the array salesPersonList is:

  43. void getData(ifstream& infile, salesPersonRec list[], int listSize) { int count; quarterType quarter; string sID; int month; double amount; infile>>sID; //Step 1 while(infile) { infile>>month>>amount; //Step 1 for(count = 0; count < listSize; count++) //Step 2 {

  44. if(sID == list[count].ID) { if(1 <= month && month <= 3) //Step 3 quarter = QT1; else if(4 <= month && month <= 6) quarter = QT2; else if(7 <= month && month <= 9) quarter = QT3; else quarter = QT4; list[count].saleByQuarter[quarter] += amount; //Step 4 break; //exit for loop }//end if }//end for infile>>sID; //Step 1 }//end while }//end getData

  45. Function saleByQuarter: void saleByQuarter(salesPersonRec list[], int listSize, double totalByQuarter[]) { quarterType quarter; int count; for(quarter = QT1; quarter <= QT4; quarter = static_cast<quarterType>(quarter+1)) totalByQuarter[quarter] = 0.0; for(quarter = QT1; quarter <= QT4; quarter = static_cast<quarterType>(quarter+1)) for(count = 0; count < listSize; count++) totalByQuarter[quarter] += list[count].saleByQuarter[quarter]; }

  46. Function totalSaleByPerson: This function finds the yearly sale amount of each salesman sale. void totalSaleByPerson(salesPersonRec list[], int listSize) { int count; quarterType quarter; for(count = 0; count < listSize; count++) //for each salesperson for(quarter = QT1; quarter <= QT4; //for each quarter quarter = static_cast<quarterType>(quarter + 1)) list[count].totalSale += list[count].saleByQuarter[quarter]; }

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