Where ampersand "&" can be put when passing argument by reference?

Both are exactly the same. No difference at all.

All that matters is that & should be between the type and the variable name. Spaces don't matter.

void AddOne(int&  y);
void AddOne(int  &y);
void AddOne(int & y)
void AddOne(int   &     y);
void AddOne(int&y);

are same!

There is no differences between

void AddOne(int &y);

and

void AddOne(int& y);

and even

void AddOne(int&y);

in C++, as the whitespaces between actual tokens are discarded.

It's the same for the language, just different code conventions

Related