I'm not sure what your question is. Are you asking about converting integers to doubles? As in, the square root in the formula would change their type?
{
int x1,x2,y1,y2;
double s;
printf("Please enter your values x1,x2,y1,y2\n");
scanf("%d%d%d%d",&x1,&x2,&y1,&y2);
s=(pow((x2-x1),2)-pow((y2-y1),2));
printf("%lf",s);