The error was thrown from the gpp-compiler package. This issue has already been reported.

[7bhainikhil]

In file included from c:\mingw\include\wchar.h:61:0,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\cwchar:44,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\bits\postypes.h:40,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\iosfwd:40,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\ios:38,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\ostream:38,
from c:\mingw\lib\gcc\mingw32\6.3.0\include\c++\iostream:39,
from F:\Apna college\C++ full course\demo.cpp:1:
c:\mingw\include\wctype.h:87:20: fatal error: stddef.h: No such file or directory
#include <stddef.h>
^
compilation terminated.

[ItzzExcel]

You are trying to compile in C++, the problem you have is that library: stddef.h is only for C, not for C++. I hope I've helped.

If you want to include that library in C++, use cstddef.

Reference: https://en.wikibooks.org/wiki/C_Programming/stddef.h