[编程入门]自定义函数求一元二次方程（易错点）

解题思路:

注意事项:

1. 开方使用sqrt函数，要加头文件math.h

2. 开方内的值必须为正，若为负，添-号

3. 求值公式的分子和分母分别加括号括起来，避免因优先级导致结果错误
   参考代码:

#include<stdio.h>
#include<math.h>
double big(double a,double b,double c,double t);
double small(double a,double b,double c,double t);
double equ(double a,double b,double c,double t);

int main()
{
    double a,b,c,t;
    scanf("%lf %lf %lf",&a,&b,&c);
    t=b*b-4*a*c;
    if(t>0){
        big(a,b,c,t);
    }
    else if(t<0){
        small(a,b,c,t);
    }
    else
        equ(a,b,c,t);
    return 0;
}
double big(double a,double b,double c,double t){
    printf("x1=%.3f x2=%.3f",((-b)+sqrt(t))/(2*a),((-b)-sqrt(t))/(2*a));
}
double equ(double a,double b,double c,double t){
    printf("x1=%.3f x2=%.3f",(-b)/(2*a),(-b)/(2*a));
}
double small(double a,double b,double c,double t){
    printf("x1=%.3f+%.3fi x2=%.3f-%.3fi",(-b)/(2*a),sqrt(-t)/(2*a),(-b)/(2*a),sqrt(-t)/(2*a));
}