它总是报错，请问怎么改啊

#include <stdio.h>
#include <math.h>
double f(float x1,float y1,float x2,float y2)
{
double distance;
distance=sqrt((x1-x2)(x1-x2)+(y1-y2)(y1-y2));
return distance;
}
{
float x1,y1,x2,y2;
printf("(x1,y1,x2,y2)\n");
scanf("%f,,&x1,&y1,&x2,&y2);
printf("%f\n",f(x1,y1,x2,y2));
}
它总是报错1 [Error] expected unqualified-id before '{' token

没有main函数

#include <stdio.h>
#include <math.h>
double f(float x1,float y1,float x2,float y2)
{
double distance;
distance=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
return distance;
}
int main()
{
float x1,y1,x2,y2;
printf("(x1,y1,x2,y2)\n");
scanf("%f,,&x1,&y1,&x2,&y2);
printf("%f\n",f(x1,y1,x2,y2));
return 0;
}

写程序，首先写入口的main函数，还有那个乘法的符号是不能省的，