pi.c

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>
#define MAX_NUM 999999999



typedef struct{
 long double ax;
 long double ay;
}position;

int get_random(int min, int max){
  return min + (int)(rand()*(max-min+1.0)/(1.0+RAND_MAX));
}

/* 任意の点の座標をランダムに取得 */
void get_position(position *pos){
  pos->ax = get_random(0,100000000)/1000000;
  pos->ay = get_random(0,100000000)/1000000;
}

/* 任意の点の座標を表示 */
void print_position(position pos){
  printf("(%.1f,%.1f)\n", pos.ax, pos.ay);
}



/* 任意の二点間の距離を出す */
long double dist_pos(position pos1, position pos2){
  long double diffx = pos1.ax - pos2.ax;
  long double diffy = pos1.ay - pos2.ay;

  return sqrt(diffx * diffx + diffy * diffy);
}

/* 半径50の円の領域内に入っているのかどうかを判定 */
int circle_include_judge(position pos){
  position cir = {50.0, 50.0};
  return 50.0 >= dist_pos(cir, pos);
}

/* πを出す */
double cal_pi(long double n1,long double n2){
  return ((long double)4 * n1) / (n1 + n2);
}

/* main関数ですよ */
int main(void){
  int i;
  position point={};
  long double n1,n2;
  n1=n2=0;

  srand((unsigned int)time(NULL));


  for(i=0;i<MAX_NUM;i++){
    get_position(&point);
     if( circle_include_judge(point)){
      n1++;
    }else{
      n2++;
    }
  }

  printf("%f\n",cal_pi(n1,n2));
  
  return 0;
}