// Note:Your choice is C++ IDE
#include "iostream.h"
#include<stdlib.h>   //定义exit()函数
#include<math.h>     //定义sqrt()、fabs()等数学函数
float x1,x2,disc,p,q;
float greater_zero(float a,float b)
{
    x1=(-b+sqrt(disc))/(2*a);
    x2=(-b+sqrt(disc))/(2*a);
}
float equal_zero(float a,float b)
{
    x1=x2=(-b)/(2*a);
    
}
float smaller_zero(float a,float b)
{
    p=(-b)/(2*a);
    q=sqrt(disc)/(2*a);

}
void main()
{
    float a,b,c;
    cin>>a>>b>>c;
    if(a=0)
    {
        
    cout<<"the single root is"<<-c/b<<endl;
    exit(1);
    }
disc=b*b-4*a*c;
if(disc>0)
{
    greater_zero(a,b);
    cout<<"x1="<<x1<<"x2="<<x2<<endl;
}
else
if(disc==0)
{
    equal_zero(a,b);
    cout<<"x1=x2="<<x1<<x2<<endl;
}
else
{
    smaller_zero(a,b);
    cout<<"x1="<<p<<"+"<<q<<"i"<<"x2="<<p<<"-"<<q<<"i";endl;
}
}
我想问一下，为什么会提示要返回一个值啊！我不是定义了全局变量吗？程序应该怎么改啊！