刚学函数定义,求两点距离,看看怎么改

刚学函数定义,求两点距离,看看怎么改#include#include double sqrt(double y2,double y1,double x2,double x1){return sqrt(pow((y2 - y1),2) + pow((x2 - x1),2));}void main(){double length,y2,y1,x2,x1; printf("This program is calculate the two porint length\nPlease input ：x1 y1 x2 y2 \n");scanf("%lf %lf %lf %lf",&x1,&y1,&x2,&y2);length=sqrt(y2,y1,x2,x1);printf("length：%lf\n",length);}老师说要，一楼的方法是Function Prototypes吗，还有Function Prototypes谁能解释一下。