29.根据公式计算值

#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
double fun(int n)
{
int i, k;
double s, t;
s = 0.0;
k = 1;
for (i = 1;i <= n;i++)
{
t = 2 * i;
s = s + k * (2 * i - 1) * (2 * i + 1) / (t*t);
k = k*(-1);
}
return s;
}
int main()
{
int n = -1;
while (n < 0)
{
printf("Please input(n>0):");
scanf("%d", &n);;
printf("\nThe result is :%f\n", fun(n));
}
getchar();
getchar();
return 0;
}