how to combine values of two fields

Hello,

I have three fields in my application form.

The first Field: Student ID
The second Field: Parent ID
The third field: ID Combination

For example:

Value of Student ID: 765
Value of Parent ID: 123

How do we combine those two values into the third field ? The example result would be in the third field is 765123

Thank You
Subhan

Using this will work

{thirdfield}={firstfield}.{secondfield};

upper post is correct. But you need to apply that in the onload