编程实现一元二次方程的解 ax^2+bx+c=0

#include "stdafx.h"
#include <iostream>
#include <cmath>
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
double a,b,c;
double delta;
double x1,x2;
cout<<"Please input a,b,c:"<<endl;
cin>>a>>b>>c;
if(cin.fail())
{
cout<<"Error:bad input!";
return 1;
}
delta=b*b-4*a*c;
if(delta>0)
{
cout<<"The Equation has two roots:"<<endl;
x1=(-b+sqrt(delta))/(2*a);
x2=(-b-sqrt(delta))/(2*a);
cout<<"x1="<<x1<<"\n"
<<"x2="<<x2<<"\n";
}
if(delta==0)
{
cout<<"The Equation has two equal roots:"<<endl;
x1=(-b+sqrt(delta))/(2*a);
cout<<"x1=x2="<<x1<<endl;
}

if(delta<0)
{
cout<<"The Equation has two virtual roots:"<<endl;
cout<<"x1="<<(-b)/(2*a)<<"+"<<sqrt(-delta)/(2*a)<<"i"<<endl;
cout<<"x2="<<(-b)/(2*a)<<"-"<<sqrt(-delta)/(2*a)<<"i"<<endl;
}
system("pause");
return 0;
}

实现算法：
 
#include "stdafx.h"
#include <iostream>
#include <cmath>
using namespace std;
int sgn(int m)
{
if(m>=0)
return 1;
else return -1;
}
int _tmain(int argc, _TCHAR* argv[])
{
double a,b,c;
double delta;
double q;
double x1,x2;
cout<<"Please input a,b,c:"<<endl;
cin>>a>>b>>c;
delta=b*b-4*a*c;
if(delta>0)
{
cout<<"The equation has two roots:"<<endl;
q=-(b+sgn(b)*sqrt(delta))/2.0;

x1=q/a;
x2=c/q;

cout<<fixed;
cout<<"x1="<<x1<<"\n"
<<"x2="<<x2<<endl;
}
if(delta==0)
{
cout<<"The equation has two equal roots:"<<endl;
q=-(b+sgn(b)*sqrt(delta))/2.0;

x1=q/a;
cout<<"x1=x2="<<x1<<endl;
}
if(delta<0)
{
cout<<"Error!"<<endl;
return 1;
}
system("pause");
retur