C :

#include<stdio.h>
#include<math.h>
 
int main(){
  int a,b,c;
  int disc;
  double p1,p2,p3;
  scanf("%d %d %d",&a,&b,&c);
  if(a==0)
    printf("not a quadratic\n");
  else{
	    disc=b*b-4*a*c;
    p1=-b/(2.0*a);
	    p2=sqrt(disc)/(2.0*a);
    p3=sqrt(-disc)/(2.0*a);
	    if(disc<0)
		      printf("complex roots:%.4lf+%.4lfi %.4lf-%.4lfi\n",p1,p3,p1,p3);
	    else if(disc==0)
		      printf("two equal roots:%.4lf\n",-b/(2.0*a));
	    else if(disc>0)
		      printf("distinct real roots:%.4lf %.4lf\n",p1+p2,p1-p2);	  
  } 
  return 0;
}

C++ :

#include <stdio.h>
#include <math.h>
int main() {
	int a, b, c, delta;
	double ans0, ans1, sqrt_delta, realpart, imagpart;
	scanf("%d %d %d", &a, &b, &c);
	/* 计算delta的值（b*b-4*a*c）并分类讨论 */
	delta = b * b - 4 * a * c;
	if (delta > 0) {
		sqrt_delta = sqrt(delta);
		ans0 = (-b - sqrt_delta) / (2.0 * a);
		ans1 = (-b + sqrt_delta) / (2.0 * a);
		printf("distinct real roots:%.4f %.4f\n", ans0, ans1);
	} else if (delta == 0) {
		ans0 = (-b) / (2.0 * a);
		printf("two equal roots:%.4f\n", ans0);
	} else {
		realpart = -b / (2.0 * a);
		imagpart = sqrt(-delta) / (2.0 * a);
		printf("complex roots:%.4f+%.4fi %.4f-%.4fi\n", realpart, imagpart, realpart, imagpart);
	}
	return 0;
}

Pascal :

var 
  a,b,c,d:double;

begin
  readln(a,b,c);
  d:=b*b-4*a*c;
  if( a<1e-8 ) then writeln('not a quadratic')
    else if( (d>0) and (d<=1e-8) ) then
     writeln('two equal roots:',-b/(2*a):0:4)
     else if(d>1e-8) then writeln( 'distinct real roots:', 
       (-b-sqrt(d))/(2*a):0:4 ,' ', (-b+sqrt(d))/(2*a):0:4 )
       else if(d<0) then writeln( 'complex roots:', 
       (-b)/(2*a):0:4,'+',sqrt(-d)/(2*a):0:4,'i ',
       (-b)/(2*a):0:4,'-',sqrt(-d)/(2*a):0:4,'i' );
end.

Java :

import java.util.*;
public class Main {
	public static void main(String args[]) {
		Scanner cin = new Scanner(System.in);
		double a,b,c;
		double d;
		double x1,x2;
		a=cin.nextInt();
		if(a==0){
			System.out.println("not a quadratic");
			return;
		}
		b=cin.nextInt();
		c=cin.nextInt();
		d=Math.pow(b, 2)-4*a*c;
		if(d==0){
			x1=-b/(2*a);
			System.out.printf("two equal roots:%.4f\n",x1);
		}
		else if(d>0){
			x1=(-b+Math.sqrt(d))/(2*a);
			x2=(-b-Math.sqrt(d))/(2*a);
			System.out.printf("distinct real roots:%.4f %.4f\n",x1,x2);
		}
		else {
			d=-d;
			x1=(-b)/(2*a);
			x2=Math.sqrt(d)/(2*a);
			System.out.printf("complex roots:%.4f+%.4fi %.4f-%.4fi\n",x1,x2,x1,x2);
		}
	}
}