The C language represents numbers in three forms:
This distinction reflects similar distinctions in the instruction set architecture of most central processing units. Integral data types store numbers in the set of integers, while real and complex numbers represent numbers (or pair of numbers) in the set of real numbers in floating point form.
All C integer types have signed and unsigned variants. If signed or unsigned is not specified explicitly, in most circumstances signed is assumed. However, for historic reasons plain char is a type distinct from both signed char and unsigned char. It may be a signed type or an unsigned type, depending on the compiler and the character set (C guarantees that members of the C basic character set have positive values). Also, bit field types specified as plain int may be signed or unsigned, depending on the compiler.