My favorite C "quirk": If you have an array and you want to access an item of it, you can swap the variable and the index number (put the variable name inside brackets and the number outside):

    a[5] 

is the same as:

    5[a]

why?

    a[5] is actually sugar for *(a + 5), so by commutative property, you can also do *(5 + a) to access the same memory position :-)