CSI 221 Programming 2
1
Defining the Class
class smallobj
//define a class
{
private:
int somedata;
//class data
public:
void setdata(int d) //member function to set data
{ somedata = d; }
void showdata() //member function to display data
{ cout << “Data is “ << somedata << endl; }
};
2
int main()
{
smallobj s1, s2;
//define two objects of class smallobj
s1.setdata(1066);
//call member function to set data
s2.setdata(1776);
s1.showdata(); //call member function to display data
s2.showdata();
return 0;
}
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5
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7
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OUTPUT:
10
11
12
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15
16
17
Destructors
•
A destructor function is called automatically
when an object is destroyed.
• A destructor has the same name as the constructor
(which is the same as the class name) but is
preceded by a tilde ‘~’:
class Foo
{
private:
int data;
public:
Foo() : data(0) //constructor (same name as class)
}{
~Foo()
//destructor (same name with tilde)
}{
};
18
Objects as Function Arguments
#include <iostream>
using namespace std;
////////////////////////////////////////////////////////////////
class Distance
//English Distance class
{
private:
int feet;
float inches;
public:
//overload constructor (no args)
Distance() : feet(0), inches(0.0) } {
//constructor (two args)
Distance(int ft, float in) : feet(ft), inches(in) } {
void getdist()
//get length from user
{
cout << “\nEnter feet: “; cin >> feet;
cout << “Enter inches: “; cin >> inches;
}
void showdist()
//display distance
{ cout << feet << “\’ -” << inches << ‘ \” ’; }
void add_dist( Distance, Distance );
};
//declaration
20
void Distance :: add_dist(Distance d2, Distance d3)
{
inches = d2.inches + d3.inches;
//add the inches
feet = 0;
//(for possible carry)
if( inches >= 12.0) //if total exceeds 12.0, then decrease
inches
{ inches = inches - 12.0;
//by 12.0 and
feet++;
//increase feet by 1
}
feet += d2.feet + d3.feet;
//add the feet
}
///////////////////////////////////////////////////////////////////////
21
int main()
{
Distance dist1, dist3;
Distance dist2(11, 6.25);
//define two lengths
//define and initialize dist2
dist1.getdist();
//get dist1 from user
dist3.add_dist(dist1, dist2);
//dist3 = dist1 + dist2
//display all lengths
cout << “\ndist1 = “; dist1.showdist();
cout << “\ndist2 = “; dist2.showdist();
cout << “\ndist3 = “; dist3.showdist();
cout << endl;
return 0;
}
RUN:
Enter feet: 17
Enter inches: 5.75
dist1 = 17’-5.75”
dist2 = 11’-6.25”
dist3 = 29’-0”
22
Member Functions Defined Outside the Class
void Distance :: add_dist ( Distance d2 , Distance d3 )
{
---------23
}
Objects as Arguments
24
Structures and Classes
Structure
Class
The members are public
by default
as a way to group both
data and functions
the members are private
by default
struct foo
{
void func();
private:
int data1;
};
class foo
{
int data1;
public:
void func();
};
as a way to group data
.
25
Classes, Objects, and Memory
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Static Class Data
1. Each object contains its own separate data ( variables).
2. If a data item in a class is declared as static, only one such item
is created for the entire class, no matter how many objects there are.
3. static data item is useful when all objects of the same class must
share a common item of information
27
Static versus automatic member variables
28
class foo
{
private:
static int count;
//only one data item for all objects
//note: “declaration” only!
public:
foo()
//increments count when object created
{ count++; }
int getcount()
//returns count
{ return count; }
};
///////////////////////////////////////////////////////////////////////////////////////////////////////
int foo::count = 0;
//*definition* of count
int main()
{
foo f1, f2, f3;
//create three objects
cout << “count is “ << f1.getcount() << endl;
//each object
cout << “count is “ << f2.getcount() << endl;
//sees the
cout << “count is “ << f3.getcount() << endl;
//same value
return 0;}
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Here’s the output:
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