ex8_9.cpp

来自「C++程序设计课本源码,供学习计算机的大学生们参考」· C++ 代码 · 共 43 行

#include<iostream.h>
#include<math.h>

class Simpson{
	double Intevalue,a,b;//Intevalue积分值，a积分下限，b积分上限
public:
	virtual double fun(double x)=0;//被积函数声明为纯虚函数
	Simpson(double ra=0,double rb=0){
		a=ra;
		b=rb;
		Intevalue;
	}
	void Integrate(){
		double dx;
		int i;
		dx=(b-a)/2000;
		Intevalue=fun(a)+fun(b);
		for(i=1;i<2000;i+=2)Intevalue+=4*fun(a+dx*i);
		for(i=2;i<2000;i+=2)Intevalue+=2*fun(a+dx*i);
		Intevalue*=dx/3;
	}
	void Print(){cout<<"积分值="<<Intevalue<<endl;}
};
class A:public Simpson{
public:
	A(double ra,double rb):Simpson(ra,rb){};
	double fun(double x){return sin(x);}
};
class B:public Simpson{
public:
	B(double ra,double rb):Simpson(ra,rb){};
	double fun(double x){return exp(x);}
};
void main(){
	A a1(0.0,3.1415926535/2.0);
	Simpson *s=&a1;
	s->Integrate();//动态
	B b1(0.0,1.0);
	b1.Integrate();//静态
	s->Print();
	b1.Print();
}