I don't know this type. Is that the biggest one from all? I think it is an integer type, right? Or is it a floating point thing? Bigger than double?
According to C99 standard, long long is an integer type which is at least 64-bit wide. There are two integer 64-bit types specified: long long int and unsigned long long int
So, yes, this is the biggest integer type specified by C language standard (C99 version).
There is also long double type specified by C99. It's an extended precision floating point numeric data type long for 80-bits on most popular x86-based platforms and implementations of C language.
The short and simple is that a long long is an int that is at least 64 bits wide. The rationale for this is here. Basically, it is a response to 64 bit architecture and backwards compatibility. And the name long long was deemed the least bad of all possibilities by the standards committee.
来源：https://stackoverflow.com/questions/2127473/what-kind-of-data-type-is-long-long