Answer by es1024 for Tips for golfing in C

Use *a instead of a[0] for accessing the first element of an array.

Relational operators (!=, >, etc.) give 0 or 1. Use this with arithmetic operators to give different offsets depending on whether the condition is true or false: a[1+2*(i<3)] would access a[1] if i >= 3 and a[3] otherwise.