l3_7.cpp

《C++程序设计教程》电子教案及例题源码

#include  "iostream.h"
#include  "math.h"
void main()
{
	double a,b,c,disc,x1,x2,p,q;
	cin >> a >> b >> c;
	if(fabs(a) < 1e-6)
		cout << "不是一元二次方程" << endl;
	else
	{
		disc=b*b-4*a*c;
		if (fabs(disc)<=1e-6)   //有两个相等的实根
			cout << "x1=x2=" << -b/(2*a) << endl;	
		else
		{ 
			if (disc>1e-6)   // 有两个不相等的实根
			{
				x1=(-b+sqrt(disc))/(2*a);		
				x2=(-b-sqrt(disc))/(2*a);
				cout << "x1= " << x1 << endl;
				cout << "x2= " << x2 << endl;
			}
			else   //  有两个共轭复根
			{
				p=-b/(2*a);			
				q=sqrt(fabs(disc))/(2*a);
				cout << "x1= " << p << "+" << q << "i" << endl;	
				cout << "x2= " << p << "-" << q << "i" << endl;	
			}
		}
	}
}