1. CS31 Discussion 1D Winter18: week 6
TA: Behnam Shahbazi
Some slides former TAs: Chelsea Ju

2. Struct Motivation Syntax: Declaration & Initialization:
Allow user-defined data type that contains a collection of different data type
Syntax:
struct TypeName{
member1;
member2; };
Declaration & Initialization:
TypeName varName = {var1, var2};

3. Struct Motivation Example:
Allow user-defined data type that contains a collection of different data type
Example:
#include <iostream>
using namespace std;
struct date{
int day;
int month;
int year; };
int main () {
date birthday = {10, 10, 1990};
date yesterday;
yesterday.year = 2015;
yesterday.month = 3;
yesterday.day = 5; }
Don’t forget the semicolon

4. Struct Valid Operation Invalid Operation Assignment Function Argument
Ex:
date tomorrow = {7, 3, 2015};
date examDate = tomorrow;
Function Argument
Call-by-value
Call-by-reference
Return Value
Invalid Operation
Arithmetic
Comparison
I/O

5. Struct Access the member variable in struct
As a normal variable: “.” operator
As a pointer variable: “->” operator
Ex:
#include <iostream>
using namespace std;
int main () {
struct date{
int day;
int month;
int year; };
date birthday, *pbirthday;
birthday = {10, 10, 1990};
pbirthday = &birthday;
cout << birthday.day << endl;
cout << pbirthday -> month << endl;
cout << (*pbirthday).year << endl; }

6. Class Very similar to struct Except…
All the member variables and member functions are public in struct, but private in class by default
struct employee {
int ID;
double salary;
string jobtitle;
void raise(){
salary *= 1.5; } };
class employee {
int ID;
double salary;
string jobtitle;
void raise(){
salary *= 1.5; } };

7. Public vs Private Public: Private: Ex:
Public members can be used directly by objects of other classes
Private:
Private members that are hidden from other classes
It is only accessible in its member function
Ex:
#include <iostream>
int main(){
#include <string>
employee emp;
using namespace std;
emp.ID = 100;
emp.jobtitle = "Student";
class employee {
private:
emp.salary = ; //not allow
double salary;
public:
int ID;
emp.setSalary(1000.0);
string jobtitle;
//use member function to set value
void setSalary(double s){
salary = s; }
return 0; };

8. Member Function Define outside the class Define inside the class
Syntax
Classname::functionName()
Define inside the class
functionName()
class employee {
private:
double salary;
public:
int ID;
string jobtitle;
void setSalary(double s); };
void employee::setSalary(double s){
salary = s; }
class employee {
private:
double salary;
public:
int ID;
string jobtitle;
void setSalary(double s){
salary = s; } };

9. const Function A member function that can’t change the object Syntax
functionName() const
Ex:
class employee {
private:
double salary;
public:
int ID;
string jobtitle;
double getSalary(){
salary *= 1.5;
return salary; }
double getSalary() const{
salary *= 1.5; // not allow: complier error };

10. Class Constructors
A function that is automatically called when a class instance (object) is created or declared
It does NOT have any return value
Ex:
#include <iostream>
#include <string>
using namespace std;
class employee {
private:
double salary;
public:
int ID;
string jobtitle;
employee(){
ID = 1;
jobtitle = “student”;
salary = 0; } };

11. Class Constructors Constructors can also have arguments Ex:
#include <iostream>
#include <string>
using namespace std;
class employee {
private:
double salary;
public:
int ID;
string jobtitle;
employee(int e_id, sting pos, double pay){
ID = e_id;
jobtitle = pos;
salary = pay; } };

12. Class Constructors Multiple Constructors (Overload) Ex: Default
class employee {
private:
double salary;
public:
int ID;
string jobtitle;
employee(){
ID = 1;
jobtitle = “student”;
salary = 0; }
employee(int e_id, sting pos, double pay){
ID = e_id;
jobtitle = pos;
salary = pay; };
Default
Constructor
Overloaded Constructor

13. Practice Time!
Worksheet 4
Make teams of 2 people