Generally speaking, integer constants are stored as int types. If the integer constant we use is beyond the range of int, C language stipulates that the compiler automatically uses unsigned int to deal with this constant. If unsigned is not enough to represent this constant, the compiler will use long. If you still can't express it, then use unsigned long, long long and unsigned long in turn. If the unsigned long long cannot be expressed, then the compiler is helpless. Note: long long and unsigned long long are unique to C99.