double accrueInterest(double *balanceAccrue, int periodsAccrue, double rateAccrue) {
    double a = 0.0;

    rateAccrue /= 100;
    a = *balanceAccrue*pow(1 + (rateAccrue/12), periodsAccrue);     /* compound interest formula */
    a = a - *balanceAccrue;                                         /*to get just interest not interest + initial amount */
    return a;
}