#include <stdio.h>
  //正の奇数nを引数とし、n以下の正の奇数の和を求める関数
  int rec(int n)
  {
     if (n == 1)
   {
        return 1; // n=1のとき、和は 1
     }
    else
     {
         return n+rec(n - 2); // n 以下の奇数の和 = (n-2) 以下の奇数の和 + n
    }
 }
 
 int main(void)
 {
     int n = 11;
     printf("%d以下の正の奇数の和は%d\n", n, rec(n));
     return 0;
 }
// 実行結果: 11以下の正の奇数の和は36 (1+3+5+7+9+11 = 36)

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