/*フィボナッチ数列*/
/*a(n+2)=a(n+1)+an*/

#include "stdafx.h"
#include <conio.h>

int _tmain(int argc, _TCHAR* argv[])
{
    int i,n;
	int an,an1,an2;

    printf("n=20\n");

    an = 1;
    an1 = 1;  

	printf("a(1)=%d\n",an);
    for (i=2; i<=20; i++) 
	{
        an2=an1+an;       
        an=an1; 
        an1=an2;

        printf("a(%d) = %d\n", i, an);
    }
    getch();
    return 0; 
}

結果例

n=20
a(1)=1
a(2) = 1
a(3) = 2
a(4) = 3
a(5) = 5
a(6) = 8
a(7) = 13
a(8) = 21
a(9) = 34
a(10) = 55
a(11) = 89
a(12) = 144
a(13) = 233
a(14) = 377
a(15) = 610
a(16) = 987
a(17) = 1597
a(18) = 2584
a(19) = 4181
a(20) = 6765