Hi,
Please try below code.
C#
string StrAnnualSalary = "20398.00";
double averagemonthbasictemp = Math.Round(Convert.ToDouble(StrAnnualSalary) / 12,2);
VB
Dim StrAnnualSalary As String = "20398.00"
Dim averagemonthbasictemp As Double = Math.Round(Convert.ToDouble(StrAnnualSalary) / 12, 2)
I hope this will help you out.