C++ :

#include<cstring>
#include<cstdio>
using namespace std;
 
double ans[4];
double a,b,c,d;
double f(double xt)
{
    double s;
    s=xt*xt*xt+b*xt*xt+c*xt+d;
    return s;
}
int main()
{
    scanf("%lf%lf%lf%lf",&a,&b,&c,&d);
    b/=a; c/=a; d/=a;
    double x1,x2; int p=0;
    for (int x=-10000;x<=10000;x++)
    {
        x1=(x-0.05)/100.0; x2=(x+0.05)/100.0;
        if (f(x/100.0)==0 || f(x1)*f(x2)<0)
        {
            p++; ans[p]=x/100.0;
        }
        if (p==3) break;
    }
    for (int i=1;i<=2;i++)
        for (int j=2;j<=3;j++)
            if (ans[i]>ans[j])
            {
                double t=ans[i];ans[i]=ans[j];ans[j]=t;
            }
    for (int i=1;i<=p-1;i++)
        printf("%.2lf ",ans[i]);
    printf("%0.2lf",ans[p]);
    return 0;
}

Pascal :

var
	a,b,c,d,x,tmp:real;  
	ansx,f:array[1..3] of real;
	i,j:integer;

	begin
		readln(a,b,c,d);
		for i:=1 to 3 do
		f[i]:=1e12;
		x:=-100;
		while(x<=100) do
		begin
			tmp:=(d+x*(c+x*(b+x*a)));
			j:=1;
			for i:=2 to 3 do
				if (f[i]>f[j]) then j:=i;
			if (abs(tmp)<f[j]) then
			begin
				f[j]:=abs(tmp);
				ansx[j]:=x;
			end;
			x:=x+0.01;
		end;
		for i:=1 to 3 do
			for j:=i+1 to 3 do
				if (ansx[i]>ansx[j]) then
				begin
					tmp:=ansx[i];
					ansx[i]:=ansx[j];
					ansx[j]:=tmp;
				end;
		writeln(ansx[1]:0:2,' ',ansx[2]:0:2,' ',ansx[3]:0:2);
	end.