参考（要确保数据合法）

#include <stdio.h>

#include <math.h>

int main(int argc, char* argv[])

{

double a,b,c,p,q,x1,x2;

scanf("%lf%lf%lf",&a,&b,&c);

p=-b/(2*a);

q=sqrt(b*b-4*a*c)/(2*a);

x1=p+q;

x2=p-q;

printf("%lf %lf",x1,x2);

return 0;

}

算法的“式子”题目中已经有了，下面按此算法写出的c++源程序：#include <iostream>#include <cmath>using namespace std;#define ESSP 0.00000001int main(){ double a,b,c,delta,p,q,x1,x2; cout<<"Input a,b,c:"; cin>>a>>b>>c; delta=b*b-4*a*c; p=-b/(2*a); q=delta/(2*a); if(delta>0) { x1=p+q; x2=p-q; cout<<"This eqution has two roots:"<<"x1="<<x1<<",x2="<<x2<<endl; }else if(delta<0) cout<<"This equation has no real root."<<endl; else { x1=x2=p; cout<<"This eqution has two equalize roots:"<<"x1=x2="<<p<<endl; } return 0;}判别式大于零时的运行例：

如果只要判别式大于零时的根，可以把 else if(delta<0)起的相关语句去掉。