E.8. Suffixes for Integer and Floating-Point Constants
C++ provides integer and floating-point suffixes for specifying the types of integer and floating-point constants. The integer suffixes are: u or U for an unsigned integer, l or L for a long integer, and ul or UL for an unsigned long integer. The following constants are of type unsigned, long and unsigned long, respectively:
174u 8358L 28373ul
If an integer constant is not suffixed, its type is int; if the constant cannot be stored in an int, it is stored in a long.
A floating-point constant that is not suffixed is of type double. A constant with an improper suffix results in either a compiler warning or an error.