用typedef定义结构体

typedef struct{}XXXXXXXXXXXX;

#include<math.h>
#include<stdio.h>
typedef struct {
double a,b;
}Point;

typedef struct {
double a,b;
}Qoint;
int main()
{
    double x;
    Qoint a;
    Point b;
    scanf("%lf%lf%lf%lf",&a.a,&a.b,&b.a,&b.b);
    x=sqrt((a.a-b.a)*(a.a-b.a)+(a.b-b.b)*(a.b-b.b));
    printf("%lf",x);
    return 0;
}