CSE202: Lecture 19 The Ohio State University 1

C++ Classes

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List of circles

• Represent a list of circles:

vector<double> xlist; // x-coordinates of centers

vector<double> ylist; // y-coordinates of centers

vector<double> rlist; // circle radii

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inputCircles.cpp...int main(){ vector<double> xlist; // x-coordinates of circle centers vector<double> ylist; // y-coordinates of circle centers vector<double> rlist; // circle radii double x, y, radius; int n(0);

cout << "Enter number of circles: "; cin >> n;

for (int i = 0; i < n; i++) { cout << "Enter circle " << i << " (x, y, radius): "; cin >> x; xlist.push_back(x); cin >> y; ylist.push_back(y); cin >> radius; rlist.push_back(radius); } ...

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Class Circle

• Create an “object” (C++ class) representing a circle:

class Circle

{

public:

double x;

double y;

double radius;

};

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Attributes

• C++ class representing a circle:class Circle

{

public:

double x;

double y;

double radius;

};

• x, y, radius are called the “class attributes” or “data members” of class Circle.

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Class Attributes

• C++ class representing a circle:class Circle

{

public:

double x;

double y;

double radius;

};

• x, y, radius are called the “class attributes” or “data members” of class Circle.

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Class Attributesclass Circle

{

public:

double x;

double y;

double radius;

};

• To declare a Circle object:

Circle c;• To access the Circle attributes:

c.x

c.y

c.radius

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Example class Circle

{

public:

double x;

double y;

double radius;

};

... Circle c;

cin >> c.x; cin >> c.y; cin >> c.radius;

cout << "Radius = " << c.radius << endl;

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List of circles

• C++ class representing a circle:class Circle

{

public:

double x;

double y;

double radius;

};

• Declare a vector of class Circle:

vector<Circle> list;

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circleClass.cpp...class Circle{public: double x; // x-coordinate of circle center double y; // y-coordinate of circle center double radius; // radius of circle};

int main(){ Circle c; vector<Circle> list; int n(0);...

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circleClass.cpp... cout << "Enter number of circles: "; cin >> n;

for (int i = 0; i < n; i++) { cout << "Enter circle " << i << " (x, y, radius): "; cin >> c.x; cin >> c.y; cin >> c.radius; list.push_back(c); }

cout << endl << "Circles:" << endl; for (int i = 0; i < list.size(); i++) { c = list[i]; cout << "Center: (" << c.x << "," << c.y << ")."; cout << " Radius: " << c.radius << endl; }...

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circleClass2.cpp...class Circle{public: double x; double y; int radius; // Note: radius is type int, not double};

int main(){ Circle c; vector<Circle> list; int n(0);...

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What’s the error?...class Circle{public: double x; // x-coordinate of circle center double y; // y-coordinate of circle center double radius; // radius of circle}

int main(){ Circle c; vector<Circle> list; int n(0);...

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circleIntersect.cpp...class Circle{public: double x; double y; double radius;};

// protoypesvoid read_circle(const char * prompt, Circle & c);bool intersects(const Circle & c1, const Circle & c2);

int main(){ Circle c1, c2;...

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circleIntersect.cpp...// protoypesvoid read_circle(const char * prompt, Circle & c);bool intersects(const Circle & c1, const Circle & c2);

int main(){ Circle c1, c2;

read_circle("Enter first circle (x,y,radius): ", c1); read_circle("Enter second circle (x,y,radius): ", c2);

if (intersects(c1, c2)) { cout << "Circles intersect." << endl; } else { cout << "Circles do not intersect." << endl; };...

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read_circle()

void read_circle(const char * prompt, Circle & c){ cout << prompt; cin >> c.x; cin >> c.y; cin >> c.radius;}

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intersects()

bool intersects(const Circle & c1, const Circle & c2){ double diffx = c1.x - c2.x; double diffy = c1.y - c2.y; double dist = sqrt(diffx*diffx + diffy*diffy);

if (dist <= c1.radius + c2.radius) { return(true); } else { return(false); }}

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What’s the error?...// protoypesvoid read_circle(const char * prompt, Circle & c);bool intersects(const Circle & c1, const Circle & c2);

class Circle{public: double x; double y; double radius;};

int main(){ Circle c1, c2;...

C++ Classes

• Class definition should always be followed by a semicolon:

class Circle{

...

}; // <-Note: semicolon

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C++ Classes

• C++ classes should usually be passed by reference. (Why?);

• Use const if the C++ class is not changed inside the function;

• Declare C++ classes before function prototypes.

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Class Circle

class Circle{public: double x; // x-coordinate of circle center double y; // y-coordinate of circle center double radius; // radius of circle};

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New Class Circle

class Point{public: double x; // x-coordinate double y; // y-coordinate};

class Circle{public: Point center; // circle center double radius; // circle radius};

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circleContains.cpp...int main(){ Circle c; Point p;

cout << "Enter point (x,y): "; cin >> p.x; cin >> p.y;

cout << "Enter circle (x,y,radius): "; cin >> c.center.x; cin >> c.center.y; cin >> c.radius;...

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Classes Containing Classes• Access the attributes x and y of class center as:

c.center.x c.center.y

• For instance:

cout << "Enter circle (x,y,radius): "; cin >> c.center.x; cin >> c.center.y; cin >> c.radius;

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circleContains.cpp... double diffx = p.x - c.center.x; double diffy = p.y - c.center.y; double dist = sqrt(diffx*diffx + diffy*diffy);

if (dist <= c.radius) { cout << "Point is inside circle." << endl; } else { cout << "Point is not inside circle." << endl; }

return 0;}

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circleContains2.cpp...class Point{public: double x; double y;};

class Circle{public: Point center; double radius;};

void read_point(const char * prompt, Point & p);void read_circle(const char * prompt, Circle & c);double compute_distance(const Point & p1, const Point & p2);...

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circleContains2.cpp...int main(){ Circle c; Point p;

read_point("Enter point (x,y): ", p); read_circle("Enter circle (x,y,radius): ", c);

double dist = compute_distance(p, c.center); if (dist <= c.radius) { cout << "Point is inside circle." << endl;} else { cout << "Point is not inside circle." << endl; }

return 0;}...

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read_circle() and read_point()

void read_circle(const char * prompt, Circle & c){ cout << prompt; cin >> c.center.x; cin >> c.center.y; cin >> c.radius;}

void read_point(const char * prompt, Point & p){ cout << prompt; cin >> p.x; cin >> p.y;}

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compute_distance()

double compute_distance(const Point & p1, const Point & p2){ double diffx = p1.x - p2.x; double diffy = p1.y - p2.y; double dist = sqrt(diffx*diffx + diffy*diffy);

return(dist);}

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compute_distance()• Note: Function compute_distance() has no idea that p2 is

the center of a circle.

...int main(){... double dist = compute_distance(p, c.center);...}

double compute_distance(const Point & p1, const Point & p2){ double diffx = p1.x - p2.x; double diffy = p1.y - p2.y; double dist = sqrt(diffx*diffx + diffy*diffy);

return(dist);}

Comparing Line Segments

• Write a program to read in two line segments and report which one is longer.

• Each line segment has two endpoints;

• Each endpoint has two coordinates.

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Class LineSegment

class Point{public: double x; double y;};

class LineSegment{public: Point endpoint1; Point endpoint2;};

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lineSegment.cpp...void read_point(const char * prompt, Point & p);void read_line_segment (const char * header, LineSegment & seg);double compute_distance (const Point & p1, const Point & p2);

int main(){ LineSegment segA; LineSegment segB;

read_line_segment("Enter first line segment: ", segA); read_line_segment("Enter second line segment: ", segB);...

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lineSegment.cpp... double length1 = compute_distance(segA.endpoint1, segA.endpoint2); double length2 = compute_distance(segB.endpoint1, segB.endpoint2);

if (length1 > length2) { cout << "First line segment is longer." << endl; } else if (length2 > length1) { cout << "Second line segment is longer." << endl; } else { cout << "Line segments have equal length." <<

endl; }

return 0;}...

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read_point() and read_line_segment()

void read_point(const char * prompt, Point & p){ cout << prompt; cin >> p.x; cin >> p.y;}

void read_line_segment (const char * heading, LineSegment & seg){ cout << heading << endl; read_point ("Enter first endpoint (x,y): ", seg.endpoint1); read_point ("Enter second endpoint (x,y): ", seg.endpoint2);}

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compute_distance()

• Note: Function compute_distance() has no idea that p2 and p2 are line segment endpoints.

... double length1 = compute_distance(segA.endpoint1, segA.endpoint2); double length2 = compute_distance(segB.endpoint1, segB.endpoint2);...

double compute_distance(const Point & p1, const Point & p2){ double diffx = p1.x - p2.x; double diffy = p1.y - p2.y; double dist = sqrt(diffx*diffx + diffy*diffy);

return(dist);}

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lineSegment2.cpp

class Point{public: double x; double y;};

class LineSegment{public: Point endpoint[2]; // Declare endpoints as an array};

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lineSegment2.cpp... double length1 = compute_distance(segA.endpoint[0], segA.endpoint[1]); double length2 = compute_distance(segB.endpoint[0], segB.endpoint[1]);

if (length1 > length2) { cout << "First line segment is longer." << endl; } else if (length2 > length1) { cout << "Second line segment is longer." << endl; } else { cout << "Line segments have equal length." <<

endl; }

return 0;}...

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lineSegment2.cpp

void read_point(const char * prompt, Point & p){ cout << prompt; cin >> p.x; cin >> p.y;}

void read_line_segment (const char * heading, LineSegment & seg){ cout << heading << endl; read_point ("Enter first endpoint (x,y): ", seg.endpoint[0]); read_point ("Enter second endpoint (x,y): ", seg.endpoint[1]);}

Class Person

class Person {

public:

int age;

double height;

double weight;

bool gender;

string first_name;

string last_name;

};

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