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  1. #include <stdio.h>
  2. // a[n] = 2a[n-1] + a[n-2], a[1]=2, a[2]=3（再帰なし版）
  3.  
  4. int main(void) {
  5.     int n = 4;
  6.     int a, b = 3, c = 2; 
  7.     for(int i = 3; i <= n; i++){
  8.         a = 2*b + c;
  9.         c = b;   // 先に c に旧 b の値を入れる
  10.         b = a;   // その後 b に新しい a を入れる
  11.     }
  12.     printf("数列a%dの値は%d\n", n, a);
  13.     return 0;
  14. }
Success #stdin #stdout 0s 5316KB
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Standard input is empty
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数列a4の値は19
https://ideone.com/xDbXM8
language:
C (gcc 8.3)
created:
1 day ago
visibility:
public

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