c# - How can i throw exception to the value from app.config file -

i said import sales tax rate app.config file. in app.config file have 2 tax value gst , pst. how can import string value program code plus convert decimal value , add . have done till , receiving error of throw exception. how can throw exception ?? in advance.

public decimal salestax          {                         {                 decimal rategst = decimal.parse(configurationmanager.appsettings["rategst"]);                 decimal ratepst = decimal.parse(configurationmanager.appsettings["ratepst"]);                 return subtotal * (rategst + ratepst);             }         } 

my app.config file below

<?xml version="1.0" encoding="utf-8" ?> <configuration>   <appsettings>      <!--government sales tax-->     <add key ="rategst" value="5"/>      <!--provincial sales tax-->     <add key="ratepst" value="8"/>    </appsettings> </configuration> 

try following

using system; namespace demo {     class class1     {         public decimal subtotal { get; set; } //= 5;         public decimal salestax         {                         {                 decimal rategst = decimal.parse(properties.settings.default.rategst);                 decimal ratepst = decimal.parse(properties.settings.default.ratepst);                 decimal result = subtotal * (rategst + ratepst);                 return result;             }         }     } }