ex6_20.cpp

纯粹是学习专用～

#include <iostream.h>                                                    
#include <iomanip.h>
                                                      
double f1(double x){
	return (1+x+2*x*x);
}
double f2(double x){
	return (1+x+2*x*x+3*x*x*x);
}
double f3(double x){
	return (1+x+2*x*x+3*x*x*x+4*x*x*x*x);
}
double integer (double (*func)(double),float, float);
void main(){
	double fixint1, fixint2, fixint3;
	fixint1=integer(f1,0.0,3.0);
	fixint2=integer(f2,0.0,3.0);
	fixint3=integer(f3,0.0,3.0);
	cout<<fixint1<<'\n'<<fixint2<<'\n'<<fixint3<<'\n';
}
double integer (double (*func)(double),float a,float b){
	double result,step;
	result=((func)(a)+(func)(b))/2;//亦可用(*func)
	step=(b-a)/100;
	for (int i=1;i<100;i++) result+=(func)(a+i*step);//亦可用(*func)
	result*=step;
	return result;
}