1. CS 1430: Programming in C++

2. Class Method Read class Student { private: string id;
string firstName, lastName;
float gpa;
public:
// Will the method change any data members?
// Yes!
void Read()
cin >> id >> firstName >> lastName >> gpa; } };

3. Class Method Write class Student { private: string id;
string firstName, lastName;
float gpa;
public:
// Will the method change any data members?
// NO!
void Write()
cout << setw(6) << id
<< setw(15) << firstName
<< setw(15) << lastName
<< setw(8) << gpa; } };

4. Class Method Modifier const
class Student {
private:
string id;
string firstName, lastName;
float gpa;
Public:
// The method will NOT change any data members: const.
void Write() const
cout << setw(6) << id
<< setw(15) << firstName
<< setw(15) << lastName
<< setw(8) << gpa; }
// The method will change data members: no const.
void Read()
cin >> id >> firstName >> lastName >> gpa; };

5. Class Method Modifier const
class Student {
private:
string id;
string firstName, lastName;
float gpa;
public:
void Write() const
float getGPA() const
string getFirst() const
// No const
void Read()
void setGPA( float value )
void updateGPA( float amount )
. . . };

6. Comparing Objects Student s1, s2; // Input data s1.Read(); s2.Read();
//Comparing GPAs of s1 and s2
if (s1.getGPA() > s2.getGPA())
cout << s1.getFirst() << “ has higher GPA.”;
else if (s1.getGPA() < s2.getGPA())
cout << s2.getFirst() << “ has higher GPA.”;
else
cout << s1.getFirst()
<< “ has the same GPA as ”
<< s2.getFirst();

7. Comparing GPA without getGPA
Student s1, s2;
// Input data
s1.Read();
s2.Read();
//Comparing GPAs of s1 and s2
if ( ? )
cout << s1.getFirst() << “ has higher GPA.”;
else if ( ? )
cout << s2.getFirst() << “ has higher GPA.”;
else
cout << s1.getFirst()
<< “ has the same GPA as ”
<< s2.getFirst();
Need a New Method!

8. Class Method HasHigherGPAThan
class Student {
private:
string id;
string firstName, lastName;
float gpa;
public:
float getGPA() const
string getFirst() const
void Read()
// Parameter is of class Student
bool HasHigherGPAThan( Student s )
if ( gpa > s.gpa )
return true;
else
return false; } };

9. Class Method HasHigherGPAThan
class Student {
private:
string id;
string firstName, lastName;
float gpa;
public:
/* Correct but not good.
bool HasHigherGPAThan( Student s )
if ( gpa > s.gpa )
return true;
else
return false; } */
// Much better!
return gpa > s.gpa; };

10. Comparing GPA without Knowing GPA
Student s1, s2;
// Input data
s1.Read();
s2.Read();
// Comparing GPAs of s1 and s2
if ( s1.HasHigherGPAThan(s2) )
cout << s1.getFirst() << “ has higher GPA.”;
else if (s2.HasHigherGPAThan(s1) )
cout << s2.getFirst() << “ has higher GPA.”;
else
cout << s1.getFirst()
<< “ has the same GPA as ”
<< s2.getFirst();
Don’t know the gpa of s1 or s2!

11. Class Method HasHigherGPAThan
class Student {
private:
string id;
string firstName, lastName;
float gpa;
public:
// Does it change any data member?
// NO!
bool HasHigherGPAThan( Student s )
return gpa > s.gpa; } };

12. Class Method HasHigherGPAThan
class Student {
private:
string id;
string firstName, lastName;
float gpa;
public:
// Will not change any data member: const
bool HasHigherGPAThan( Student s ) const
return gpa > s.gpa; } };
Passing Object as Parameter.

13. Passing Parameters Basic Data Types (char, int, float, string, bool)
Pass by Value (without & in prototype)
Pass by Reference (with & in prototype)
Arrays (of any data type)
Always Pass by Reference
(Never &)
Class Object (and structure)
C++ allows pass by value (no &) and by reference (&)
Our Rule: Always pass by reference with &
Use const for in parameter

14. Passing Object as Parameter
class Student {
private:
string id;
string firstName, lastName;
float gpa;
public:
// Will not change any data member: const
// Will not change parameter s: const with &
bool HasHigherGPAThan( const Student& s ) const
return gpa > s.gpa; } };

15. Each array element of students[] is the same as variable s.
Array of Objects
const int MAX_SIZE = 35;
int numStudents;
// parallel array to keep students’ data
float scores[MAX_SIZE];
string firstNames[MAX_SIZE];
// 35 Students
Student students[MAX_SIZE];
// Single class object
Student s;
Each array element of students[] is the same as variable s.

16. Array of Objects const int MAX_SIZE = 35; int numStudents;
Student s, students[MAX_SIZE];
// Input data
s.Read();
students[0].Read();
// Output data
s.Write();
students[1].Write();
// Update GPA
s.UpdateGPA(0.2);
students[index].UpdateGPA(0.5);

17. const int MAX_SIZE = 35;
class Student { };
int main()
int numStudents;
Student s, students[MAX_SIZE];
cin >> numStudents;
for (int i = 0; i < numStudents; i ++)
students[i].Read();
. . .
return 0; }

18. Using a function to read data to an array of Student
Function Prototype
Function Name
InputToStudentArray
Function Type
void
Parameters
s[] : array of Student
size: int, number of students of s[]
// Parameters: (Out, Out)
void InputToStudentArray(Student s[], int& size);

19. //--------------------------------------------------
// The function inputs value of size and then reads
// data for size students into array s[].
// Parameters: (Out, Out)
void InputToStudentArray(Student s[], int& size) {
cin >> size;
for (int i = 0; i < size; i++)
s[i].Read();
return; }

20. //--------------------------------------------------
// The function displays data of size students
// of array s[].
// Parameters: (In, In)
void PrintStudentArray(const Student s[], int size) {
for (int i = 0; i < size; i++)
s[i].Write();
return; }

21. //--------------------------------------------------
// The function returns the index of the first
// array element of s[] that has the same
// firstName and lastName as student m.
// Parameters: (In, In, In)
int FindStudent(const Student s[], int size,
const Student& m) {
for (int i = 0; i < size; i++)
if (s[i].getFirst() == m.getFirst() &&
s[i].getLast() == m.getLast())
return i;
return -1; }

22. const int MAX_SIZE = 35;
class Student { };
void InputToStudentArray(Student s[], int& size);
void PrintStudentArray(const Student s[], int size);
int FindStudent(const Student s[], int size, const Student& m);
int main()
. . .
return 0; }
// Function definitions

23. void InputToStudentArray(Student s[], int& size);
void PrintStudentArray(const Student s[], int size);
int FindStudent(const Student s[], int size, const Student& m);
int main() {
int numStudents, index;
Student students[MAX_SIZE];
InputToStudentArray(students, numStudents);
PrintStudentArray(students, numStudents);
Student s(“Qi”, “Yang”, 2.9);
index = FindStudent(students, numStudents, s);
students[index].UpdateGPA(1.0);
return 0; }

24. Starting Tuesday evening
Schedule
Quiz7-2
Due today by 10 PM
Quiz7-4
Due Wednesday by 10 PM
Lab 8
3 points by 5 PM, Tuesday
Lab 9
Starting Tuesday evening

25. Pair Signup by Wednesday
Schedule
Prog4
Grace Time: 10 PM, Tuesday
Prog5
Must do it in pairs!
Pair Signup by Wednesday