Does GCC support:
long long int
which would be a 64-bit integer?
Also, is long long int part of the standard?
Yes GCC does support long long int, which is a part of C99 standard.
The standard does not mandate its size in bits, but required values of LLONG_MIN and LLONG_MAX in imply it's at least 64-bit (exact 64-bit wide integer types are int64_t/uint64_t from ).
LLONG_MIN must be at most -9223372036854775807LLONG_MAX must be at least 9223372036854775807