Understand the issue: Turbo C++ use c:\TURBOC3\INCLUDE as default path

You can find this in Options->Directory

Two solutions here

1. Update the PATH
2. Mount the application directory (where you extract TURBOC3 folder) (EASY)

In my case: Mr.mohit extract TURBOC3 in home/mohit/_apps directory

so i user mount C: ~/mohit/_apps/

or either you can edit your config file by this cmd gedit .dosbox/dosbox-0.74-3.conf

Thank you 😄,
"Don't Give up MEN 💪"