Integer Types
Every integer constant is given a type based on its value and the way it is expressed. You can force any integer constant to type long by appending the letter l or L to the end of the constant; you can force it to be type unsigned by appending u or U to the value. The lowercase letter l can be confused with the digit 1 and should be avoided. Some forms of long integer constants follow:
/* Long decimal constants */ 10L 79L /* Long octal constants */ 012L 0115L /* Long hexadecimal constants */ 0xaL or 0xAL 0X4fL or 0x4FL /* Unsigned long decimal constant */ 776745UL 778866LU
The type you assign to a constant depends on the value the constant represents. A constant's value must be in the range of representable values for its type. A constant's type determines which conversions are performed when the constant is used in an expression or when the minus sign (–) is applied. This list summarizes the conversion rules for integer constants.

The type for a decimal constant without a suffix is either int, long int, or unsigned long int. The first of these three types in which the constant's value can be represented is the type assigned to the constant.

The type assigned to octal and hexadecimal constants without suffixes is int, unsigned int, long int, or unsigned long int depending on the size of the constant.

The type assigned to constants with a u or U suffix is unsigned int or unsigned long int depending on their size.

The type assigned to constants with an l or L suffix is long int or unsigned long int depending on their size.

The type assigned to constants with a u or U and an l or L suffix is unsigned long int.