12.2 Integer Constant Data Types

The type of an integer constant is normally int, if the value fits in that type, but here are the complete rules. The type of an integer constant is the first one in this sequence that can properly represent the value,

1. int
2. unsigned int
3. long int
4. unsigned long int
5. long long int
6. unsigned long long int

and that isn’t excluded by the following rules.

If the constant has ‘l’ or ‘L’ as a suffix, that excludes the first two types (those that are not long).

If the constant has ‘ll’ or ‘LL’ as a suffix, that excludes first four types (those that are not long long).

If the constant has ‘u’ or ‘U’ as a suffix, that excludes the signed types.

Otherwise, if the constant is decimal (not binary, octal, or hexadecimal), that excludes the unsigned types.

Here are some examples of the suffixes.

3000000000u      // three billion as unsigned int.
0LL              // zero as a long long int.
0403l            // 259 as a long int.
2147483648       // This is of type long long int.
                 // on typical 32-bit machines,
                 // since it won’t fit in 32 bits as a signed number.
2147483648U      // This is of type unsigned int,
                 // since it fits in 32 unsigned bits.

Suffixes in integer constants are rarely used. When the precise type is important, it is cleaner to convert explicitly (see Explicit Type Conversion).

See Integer Data Types.