Get your dad a copy of the classic Scientific and Engineering C++: An Introduction With Advanced Techniques and Examples by John Barton and Lee Nackman. It was

Get your dad a copy of the classic Scientific and Engineering C++: An Introduction With Advanced Techniques and Examples by John Barton and Lee Nackman. It was written to introduce C++ to Fortran programmers using examples from scientific/mathematical domains. The fact that it is old (from 1994) makes it better suited for folks from Fortran (or other languages) since there is none of the complexity of "Modern C++" to confuse them. Check reviews on Amazon etc.