So many to choose from ...

Convert single char c into an integer:

    int value = '0' - c;

Get the length of a static string you can use sizeof() instead of strlen()

    int len1 = sizeof("hello");   // compile-time string length

A fast and simple ring buffer (borrowed from Quake code)

    UPDATE_MASK = ARRAY_SIZE - 1;
    array[i++ & UPDATE_MASK] = data;

Init all bits of a mask to 1 on any architecture:

    unsigned int flags = -1;