I have an application where i have a drop down field where the options are numbers 1 to 5, a current date field and a return date field, what i want to do is add the number of days selected plus the current date field and set them as the return date date field.

I had success using the addDay function and a static number 

This works:

1. ReturnDate = input.Delivery_Date.addDay(3);
   input.Return_Date = ReturnDate.toDate();

However because i need to use a dynamic number based off a field what i actually need is this

This doesn't Work:

1. ReturnDate = input.Delivery_Date.addDay(input.Number_Days);
   input.Return_Date = ReturnDate.toDate();

However when i do this the input from the Number_Days field is interpreted as a string and not an integer so i end up with the error below

1. Error at line number : 1 
   Mismatch data type for function addDay at argument index 1 expected data type BIGINT found dataType STRING

I looked to see if there was a function to convert string to int but i was not able to find one, does anyone know if this is possible?