In last Monday's lecture we saw both the sizeof() and strlen() functions when discussing arrays and, in particular, arrays of characters which we treated as strings. The two functions serve different roles and, so, shouldn't be confused. The function sizeof() is not really a function at all - that is, it's not a named sequence of statements that are executed when our program runs. In fact sizeof() is a syntactic sequence recognised by the C compile - at compile time. The single parameter to sizeof() may be a datatype, or the name of a variable, and the compiler generates code involving the number of bytes required to store that datatype or variable. This is done at *compile-time*. For example, the printf() call in may produce 100bytes 400bytes 8bytes, depending on the hardware/architecture being used. In contrast, the function strlen() determines the number of bytes from the beginning (address) of its parameter to the first NULL-byte found. The function is called at *run-time*, when our program is executed. For example, consider: While the value of sizeof(string) is *always* 100, but the value of strlen(string) is initially 0, then 6, then 3.