多项式求和

#include <stdio.h>
int main(){
    double sum;
    int z, n, i;
    scanf("%d", &z);
    while ( z-- ){
        scanf("%d", &n);
        sum = 0;
        if ( n&1 ){
            sum += 1;
            for ( i=2; i<n; i+=2 ){
                sum += -1.0/i+1.0/(i+1);
            }
        }
        else {
            for ( i=1; i<n; i+=2 ){
                sum += 1.0/i-1.0/(i+1);
            }
        }
        printf("%.2lf\n", sum);
    }
    return 0;
}