Calculation of Previous year

Dear Experts,

I have to get the previous year value based on the selected year. I have done the following at "On Startup" event:

var curr_year="";

curr_year = DROPDOWN_YEAR.getSelectedValue();

var prev_year="";

Further I have written the following code:

prev_year = curr_year - 1;

For the code written in bold, I am getting following error:

Error: "String" and "int" passed. The arguments of operator "-" must have the same type

To resolve this, I even tried the following code:

Convert.stringToInt(curr_year);

Convert.stringToInt(prev_year);

I browsed through various links. Few links are below:

Default system month and year

Variable selection in Dropdown

I am still not able to get the previous year value. How to do simple mathematical calculation getting rid of string/int issues?

Please help.

Thanks and Regards,

Nitesh Kumar