大一新生c语言编程题不会写啊

怎么把他这个不同的结果写出来啊，而且这个虚数用什么数据类型啊

#include "stdio.h"
#include<math.h>
#include<stdlib.h>
typedef struct complex
{
    double _Val[2]; //real、img
}complex;
complex* getResult(double a,double b,double c,complex*res){
    double delta=b*b-4*a*c;
    if(delta>=0){
        res[0]._Val[0] = (-b+sqrt(delta))/(2*a);
        res[0]._Val[1] = 0;
        res[1]._Val[0] = (-b-sqrt(delta))/(2*a);
        res[1]._Val[1] = 0;
    }else{
        double absDelta = -delta;
        double tmp = sqrt(absDelta)/(2*a);
        res[0]._Val[0] = -b/(2*a);
        res[0]._Val[1] = tmp;
        res[1]._Val[1] = -tmp;
        res[1]._Val[0] = -b/(2*a);
    }
    return res;
}
int main(){
    double a,b,c;
    complex res[2];
    while(scanf("%lf,%lf,%lf",&a,&b,&c)!=EOF){
        if(a==0){
            printf("The equation is not a quadratic\n");
            continue;
        }
        getResult(a,b,c,res);
        if(res[0]._Val[1]!=0){//复数
        printf("The quation has complex real roots:\n");
        printf("%.4lf+%.4lfi\n",res[0]._Val[0],res[0]._Val[1]);
        printf("%.4lf%.4lfi\n",res[1]._Val[0],res[1]._Val[1]);
        }else if(res[0]._Val[0]!=res[1]._Val[0]){        
            printf("The quation has distinct real roots:%.4lf and %.4lf\n",res[0]._Val[0],res[1]._Val[0]);
        }else{
            printf("The quation has two equal real roots:%.4lf\n",res[0]._Val[0]);
        }     
    }
    system("pause");
}