#include <stdio.h>
#include <math.h>

typedef struct {
  double  x; /* x座標 */
  double  y; /* y座標 */
} Point;

Point rotate3(double, Point *);
void  rotate4(double, Point *);


int main()
{
  double rad, deg;
  Point c = {1.0, 1.0}, a = {2.0, 3.0}; /* 中心と回転対象の点 */
  Point b3, b4[3];         /* 結果を入れる構造体 */
  Point pa3[2];            /* rotate3 に渡す配列 */

  printf("回転角 [度] を入力してください\n");
  scanf("%lf", &deg);
  rad = deg*M_PI/180;
  printf("回転角 %f [deg] (%f [rad])\n", deg, rad);
  
  /* ここに関数呼び出しおよび関連するコードを書く */
  pa3[0] = b4[0] = c;
  pa3[1] = b4[1] = a;  
  b3 = rotate3(rad, pa3);
  rotate4(rad, b4);

  printf("Center  : %f %f\n", c.x, c.y);
  printf("Point A : %f %f\n", a.x, a.y);
  printf("Point B (rotate3) : %f %f\n", b3.x, b3.y);       /* rotate_3関数の結果を出力 */
  printf("Point B (rotate4) : %f %f\n", b4[2].x, b4[2].y); /* rotate_4関数の結果を出力 */
  return 0;
}

Point rotate3(double rad, Point *p)
{
  double dx, dy;
  Point pnew;

  dx = p[1].x - p[0].x;
  dy = p[1].y - p[0].y;
  pnew.x = dx*cos(rad) + dy*(-sin(rad)) + p[0].x;
  pnew.y = dx*sin(rad) + dy*cos(rad) + p[0].y;
  return pnew;
}

void rotate4(double rad, Point *p)
{
  double dx, dy;

  dx = p[1].x - p[0].x;
  dy = p[1].y - p[0].y;
  p[2].x = dx*cos(rad) + dy*(-sin(rad)) + p[0].x;
  p[2].y = dx*sin(rad) + dy*cos(rad) + p[0].y;
}