>>37
#include <stdio.h>

int main (void)
{
int i;
double pi, sum, gam, a, b, c;

a = 1.0; b = 0.5; c = 1.0/3.0;
sum = b + c;
for(i=1; i<=100; i++){
pi = 4.0 * (sum += (a*=-1) / (2*i + 1) * ((b*=0.5*0.5) + (c*=1.0/9.0)));
}
printf("π≒%.8f\n", pi);

printf("γ：");
scanf("%lf", &gam);

i = 1; sum = 0.0;
while(1){
a = pi*pi/6 - (sum += (1.0/(double)i)*(1.0/(double)i));
if(a < 0)
a *= -1.0;
if(a < gam)
break;
i++;
}
printf("N = %d\n", i);

return 0;
}