Quote from sle:
We needed people that had some quantitatve skills, but nobody (with one notable exception) was even able to multiply two matrices.
So the people you interviewed did not suck in C++, they sucked in business skills (quantitative) which you required. If that's the case, that changes your story quite a bit.
It does not show that there are no good C++ developers out there. All it proves is that few developers had specific business experience matching your requirements.
), how to print out a set of elements in a two-dimensional array(eg. first three rows, last three columns), etc. Similarly, if you applied for a quantitative programming position at Goldman Sachs or D.E. Shaw, they may ask you questions about Probability Theory, Black Scholes Model, PDE, Finite Difference Methods, Topoloy, etc.