Plouffe calculation of π in C Lang

#include <stdio.h>
#include <math.h>

int main(){
    int n = 1000, i, a;
    double Pi = 0.0;

    /* case a */
    for (i=0;i<n;i++){
        Pi += (4.0/(8.0*i+1.0)-2/(8.0*i+4.0)-1.0/(8.0*i+5.0)-1.0/(8.0*i+6.0))/pow(16.0,i);
    }
    printf("Pi = %f", Pi);
    /*end of case a*/

    /* case b
    printf("Specify a number \'a\'.\n");
    scanf("%d", &a);
    for (i=0;i<a;i++){
        Pi += (4.0/(8.0*i+1.0)-2/(8.0*i+4.0)-1.0/(8.0*i+5.0)-1.0/(8.0*i+6.0))/pow(16.0,i);
    }
    printf("\nPi = %f", Pi);
    end of case b*/

    return 0;
}