//输出面积的函数
void printArea(const Shape &s)
{cout< int main() { Circle circle(12.6); //建立Circle类对象circle cout<<\ =\ printArea(circle); Rectangle rectangle(4.5,8.4); 象rectangle cout<<\ printArea(rectangle); 面积 Triangle triangle(4.5,8.4); //建立Triangle类对象 cout<<\ =\ printArea(triangle); //输出triangle的面积 return 0; } 5： #include virtual double area() const =0; }; //定义Circle(圆形)类 class Circle:public Shape {public: Circle(double r):radius(r){} virtual double area() const {return 3.14159*radius*radius;}; protected: double radius; }; //定义Square(正方形)类 class Square:public Shape {public: Square(double s):side(s){} virtual double area() const {return side*side;} protected: //输出circle的面积 //建立Rectangle类对 //输出rectangle的 //纯虚函数 //结构函数 //定义虚函数 //半径 //结构函数 //定义虚函数 double side; }; //定义Rectangle(矩形)类 class Rectangle:public Shape {public: Rectangle(double w,double h):width(w),height(h){} //结构函数 virtual double area() const {return width*height;} //定义虚函数 protected: double width,height; //宽与高 }; //定义Trapezoid(梯形)类 class Trapezoid:public Shape {public: Trapezoid(double t,double b,double h):top(t),bottom(t),height(h){} //结构函数 virtual double area() const {return 0.5*(top+bottom)*height;} //定义虚函数 protected: double top,bottom,height; //上底、下底与高 }; //定义Triangle(三角形)类 class Triangle:public Shape {public: Triangle(double w,double h):width(w),height(h){} //结构函数 virtual double area()const {return 0.5*width*height;} //定义虚函数 protected: double width,height; //宽与高 }; int main() { Circle circle(12.6); //建立Circle类对象circle Square square(3.5); //建立Square类对象square Rectangle rectangle(4.5,8.4); //建立Rectangle类对象rectangle Trapezoid trapezoid(2.0,4.5,3.2); //建立Trapezoid类对象trapezoid Triangle triangle(4.5,8.4); //建立Triangle类对象 Shape *pt[5]={&circle,&square,&rectangle,&trapezoid,&triangle}; //定义基类指针数组pt，使它每一个元素指向一个派生类对象 double areas=0.0; //areas为总面积 for(int i=0;i<5;i++) {areas=areas+pt[i]->area();} cout<<\ //输出总面积 return 0; } 第七章 1:解法一 #include {double a,b,c,s,area; cout<<\ cin>>a>>b>>c; if (a+b<=c) cerr<<\ else if(b+c<=a) cerr<<\ else if (c+a<=b) cerr<<\ else {s=(a+b+c)/2; area=sqrt(s*(s-a)*(s-b)*(s-c)); cout<<\ return 0; } 1：解法二 #include void input(double a,double b,double c) {cout<<\cin>>a>>b>>c; } void area(double a,double b,double c) {double s,area; if (a+b<=c) cerr<<\ else if(b+c<=a) cerr<<\ else if (c+a<=b) cerr<<\ else {s=(a+b+c)/2; area=sqrt(s*(s-a)*(s-b)*(s-c)); cout<<\} int main() {double a=2,b=3,c=5; input(a,b,c); area(a,b,c); return 0; } 2：解法一 #include int main() {float a[5]; cout<<\ for(int i=0;i<5;i++) cin>>a[i]; cout< cout< 2：解法二 #include cout<<\ for(i=0;i<5;i++) cin>>a[i]; cout.setf(ios::fixed); cout.precision(2); for(i=0;i<5;i++) {cout.width(10); cout< 3： #include for(int n=1;n<8;n++) cout< #include using namespace std; //VC++ 6.0要此行 //fun1函数从键盘输入20个整数，分别存放在两个磁盘文件中 void fun1() {int a[10]; ofstream outfile1(\ //分别定义两个文件流对象 if(!outfile1) //检查打开f1.dat是否成功 {cerr<<\ exit(1); } if(!outfile2) //检查打开f2.dat是否成功 {cerr<<\ exit(1); } cout<<\ for(int i=0;i<10;i++) //输入10个数存放到f1.dat文件中 {cin>>a[i]; outfile1< cout<<\ for(i=0;i<10;i++) //输入10个数存放到f2.dat文件中 {cin>>a[i]; outfile2< outfile1.close(); //关闭f1.dat文件 outfile2.close(); //关闭f2.dat文件 } //从f1,dat读入10个数，然后存放到f2.dat文件原有数据的后面 void fun2() {ifstream infile(\ //f1.dat作为输入文件 if(!infile)
c++面向对象程序设计课后习题答案（谭浩强版）
