How To calculate Interest where period is in day

Question

void calc(double Principal, double AnnualRate, int NumberOfPeriods, int CompoundType)

{

double RatePerPeriod;

AnnualRate = AnnualRate / 100;

// CompoundType Meanse Frequant

// if Frequenc monthly - CompoundType = 12

// if Frequenc Quarterly - CompoundType = 4

// if Frequenc Half Yearly - CompoundType = 2

// if Frequenc Yearly - CompoundType = 1

double i = AnnualRate / CompoundType;

int n = CompoundType * NumberOfPeriods;

RatePerPeriod = AnnualRate / NumberOfPeriods;

returnamount = Principal * Math.Pow(1 + i, n);

Earnedamount = returnamount - Principal;

// MessageBox.Show(returnamount.ToString());

}

It Complete count interest but, it require NumberOfPeriods is in years,
How can i calculate by day.