C++: delete vs. free and performance

Question

1. Consider:

   char *p=NULL;
   free(p) // or
   delete p;
   

   What will happen if I use free and delete on p?

Answer 1

On question 2:
Previous answers are excellent. But I just wanted to add something about pre-optimization. Assuming a program of moderate complexity, the 90/10 rule usually applies - i.e. 90% of the execution time is spent in 10% of the code. "Optimized" code is often harder to read and to maintain. So, always solve the problems first, then see where the bottlenecks are (profiling is a good tool).