# include <stdio.h>
# include <math.h>
int main ()
{
    int i=1;
    double s=0.0,k=1.0,n=1.0;
    while (fabs(s)>=1e-6)
    {
        s=s+k;
        n=n+2.0;
        i=-i;
        k=i/n;
    }
    s=s*4;
    printf ("s=%10.8f\n",s);
    return 0;
}
    运行结果为4.00000