Comment by WalterBright

D supports mixed C and D files in a project. The D code can call C functions and use C types, and the C code can call D functions using C types.

The D compiler will even translate C source code to D source code if you prefer! After using a mixed D/C program for a while, I bet you'll feel motivated to take the extra step and translate the C stuff to D, as the inelegance in C will become obvious :-)