In Mathematics, there is no limitation on number. But, in computer world, everything are in binary format, and there are limited amount of memory.
Different data are represented in different ways in computer memory, and have different value ranges.
Primitive data types
The C language represents numbers in three forms: integral, real and complex. 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.
Integer types
C's integer types come in different fixed sizes, capable of representing various ranges of numbers.
| Shortest form of specifier | Minimum width (bits) |
|---|---|
| _Bool | 1 |
| char | 8 |
| signed char | 8 |
| unsigned char | 8 |
| short | 16 |
| unsigned short | 16 |
| int | 16 |
| unsigned int | 16 |
| long | 32 |
| unsigned long | 32 |
| long long | 64 |
| unsigned long long | 64 |
Floating point types
The floating-point form is used to represent numbers with a fractional component. They do not, however, represent most rational numbers exactly; they are instead a close approximation. There are three types of real values, denoted by their specifiers: single precision (float), double precision (double), and double extended precision (long double). Each of these may represent values in a different form, often one of the IEEE floating-point formats.
| Type specifiers | Precision (decimal digits) | Exponent range | ||
|---|---|---|---|---|
| Minimum | IEEE 754 | Minimum | IEEE 754 | |
| float | 6 | 7.2 (24 bits) | ±37 | ±38 (8 bits) |
| double | 10 | 15.9 (53 bits) | ±37 | ±307 (11 bits) |
| long double | 10 | 34.0 (113 bits) | ±37 | ±4931 (15 bits) |
Storage class specifiers
Every object has a storage class. This specifies most basically the storage duration, which may be static (default for global), automatic (default for local), or dynamic (allocated), together with other features (linkage and register hint).
| Specifiers | Lifetime | Scope | Default initializer |
|---|---|---|---|
| auto | Block (stack) | Block | Uninitialized |
| register | Block (stack or CPU register) | Block | Uninitialized |
| static | Program | Block or compilation unit | Zero |
| extern | Program | Block or compilation unit | Zero |
| (none) | Dynamic (heap) | Uninitialized |
Type qualifiers
Types can be qualified to indicate special properties of their data. The type qualifier const indicates that a value does not change once it has been initialized. Attempting to modify a const qualified value yields undefined behavior, so some C compilers store them in rodata or (for embedded systems) in read-only memory (ROM).
