Are there significant libraries or toolkits for that task? Or other existing code? Use the language that is compatible with them. On what platforms should the program run? It is possible to write protable code with C++, but not with Visual Basic.
Also consider which language you or your colleagues are most familiar with. Generally, if these are the only choices I'd recommend C++. It's in my opinion better suited for numerical tasks and widely supported on all platforms.
Did you consider Python? In my opinion it's more handy than C++ if computing performance is not critical. The numerical and scientific libraries (numpy, scipy, matplotlib) are quite useful, too.