A programmer's joke

A CS student shows his lab assignment to the professor. The code works and even produces the correct output, but the professor mutters that the code is not OK:

— You have to choose variable names wisely. Names like i, j, foo and bar make your code unreadable. By next time, please use long, mnemonic variable names.

A few weeks later, the same student completes a new assignment and brings it to the professor. This time, his code is full of long_mnemonic_variable_i, long_mnemonic_variable_j, long_mneminic_variable_foo and long_mnemonic_variable_bar.