Demo: Copy String

Two programs build the very same string ("John, Paul, George, Joel ") a hundred million times: one with repeated strcat() calls, the other with strcpy() calls at precomputed offsets. The C code looks equally innocent in both cases, but the measured times are not close. The aim of the demo is to see that a standard library call can hide an algorithmic cost, and that knowing what a function does internally is what lets you write measurably faster code.

Together with the teaching assistant you will fill in the TODO areas in copy-string.c and copy-string-improved.c, build both programs with make, run them, and discuss why the numbers differ.