Cann't execute my test if I add __intSum function to the beanshell postprocessor - jmeter

Question

I have written a regular expression (regexpname) in my thread which returns a number Ex: 10 and when I try to use the regular expression in the BeanShell postprocessor by adding __intSum function to add a number to the regular expression out put Ex: to add 4 to the regular expression out put i.e., 10 and store the result to a variable Ex: Total, using the following function:
{__intSum(4,${regexpname},Total}
upon trying to run my test, it stops immediately with the message
"Jmeter: Uncaught exception: java.lang.NumberFormatException: For
input string: "${regexpname}".....".
Please let me know how to fix the issue:
Here is the code I have put in beanshell postprocessor:
import java.text.SimpleDateFormat;
SimpleDateFormat sdf = new SimpleDateFormat("m/dd/yyyy"); // change it according to your Date format
Date originalDate = sdf.parse(vars.get("SigDate"));
Calendar cal = Calendar.getInstance();
cal.setTime(originalDate);
${__intSum(4,${regexpname},Total)};
cal.add(Calendar.DAY_OF_YEAR, Total); // change it if you need to add something else
Date newDate = cal.getTime();
vars.put("newDepdate", sdf.format(newDate));
log.info("Original date: " + vars.get("SigDate"));
log.info("New date: " + vars.get("newDepdate"));

Answer 1

Don't inline JMeter Functions and/or variables into scripts as they can resolve into something which will cause script failure or inconsistent behaviour. Either use "Parameters" section or go for code-based equivalents
Don't use Beanshell test elements, it is recommended to switch to JSR223 Test Elements and Groovy language for any form of scripting since JMeter 3.1
Your date format looks flaky as m stands for "minutes in hour", if you need "month in year" - go for capital M
Actually you don't even need any scripting here as there is __timeShift() function since JMeter 3.2 which can do what you need, the relevant syntax would be something like:

Answer 2

Use int Total = Integer.parseInt(vars.get("regexpname"))+4; instead of ${__intSum(4,${regexpname},Total)}; in your beanshell pre processor
I have defined regexpname as 10 in test plan so its adding 14 days and storing new date in newDepdate.
For more information on beanshell please follow this link
Please let me know if it helps..