Arithmetic types
(See also type for type system overview and the list of typerelated utilities that are provided by the C library)
Boolean typeNote that conversion to _Bool does not work the same as conversion to other integer types: (bool)0.5 evaluates to 1, whereas (int)0.5 evaluates to 0. 
(since C99) 
Character types
 signed char  type for signed character representation.
 unsigned char  type for unsigned character representation. Also used to inspect object representations (raw memory).
 char  type for character representation. Equivalent to either signed char or unsigned char (which one is implementationdefined and may be controlled by a compiler commandline switch), but char is a distinct type, different from both signed char both unsigned char
Note that the standard library also defines typedef names wchar_t , char16_t, and char32_t (since C11) to represent wide characters.
Integer types
 short int (also accessible as short, may use the keyword signed)
 unsigned short int (also accessible as unsigned short)
 int (also accessible as signed int)
 This is the most optimal integer type for the platform, and is guaranteed to be at least 16 bits. Most current systems use 32 bits (see Data models below).
 unsigned int (also accessible as unsigned), the unsigned counterpart of int, implementing modulo arithmetic. Suitable for bit manipulations.
 long int (also accessible as long)
 unsigned long int (also accessible as unsigned long)

(since C99) 
Note: as with all type specifiers, any order is permitted: unsigned long long int and long int unsigned long name the same type.
The following table summarizes all available integer types and their properties:
Type specifier  Equivalent type  Width in bits by data model  

C standard  LP32  ILP32  LLP64  LP64  
short

short int  at least 16 
16  16  16  16 
short int
 
signed short
 
signed short int
 
unsigned short

unsigned short int  
unsigned short int
 
int

int  at least 16 
16  32  32  32 
signed
 
signed int
 
unsigned

unsigned int  
unsigned int
 
long

long int  at least 32 
32  32  32  64 
long int
 
signed long
 
signed long int
 
unsigned long

unsigned long int  
unsigned long int
 
long long

long long int (C99) 
at least 64 
64  64  64  64 
long long int
 
signed long long
 
signed long long int
 
unsigned long long

unsigned long long int (C99)  
unsigned long long int

Besides the minimal bit counts, the C Standard guarantees that
 1 == sizeof(char) <= sizeof(short) <= sizeof(int) <= sizeof(long) <= sizeof(long long).
Note: this allows the extreme case in which bytes are sized 64 bits, all types (including char) are 64 bits wide, and sizeof returns 1 for every type.
Note: integer arithmetic is defined differently for the signed and unsigned integer types. See arithmetic operators, in particular integer overflows.
Data models
The choices made by each implementation about the sizes of the fundamental types are collectively known as data model. Four data models found wide acceptance:
32 bit systems:
 LP32 or 2/4/4 (int is 16bit, long and pointer are 32bit)
 Win16 API
 ILP32 or 4/4/4 (int, long, and pointer are 32bit);
 Win32 API
 Unix and Unixlike systems (Linux, Mac OS X)
64 bit systems:
 LLP64 or 4/4/8 (int and long are 32bit, pointer is 64bit)
 Win64 API
 LP64 or 4/8/8 (int is 32bit, long and pointer are 64bit)
 Unix and Unixlike systems (Linux, Mac OS X)
Other models are very rare. For example, ILP64 (8/8/8: int, long, and pointer are 64bit) only appeared in some early 64bit Unix systems (e.g. Unicos on Cray).
Note that exactwidth integer types are available in <stdint.h> since C99
Real floating types
C has three types for representing real floatingpoint values:
 float  single precision floating point type. Matches IEEE754 32 bit floating point type if supported.
 double  double precision floating point type. Matches IEEE754 64 bit floating point type if supported
 long double  extended precision floating point type. Matches IEEE754 extended floatingpoint type if supported, otherwise matches some nonstandard extended floatingpoint type as long as its precision is better than double and range is at least as good as double, otherwise matches the type double. Some x86 and x86_64 implementations use the 80bit x87 floating point type.
Floatingpoint types may support special values:
 infinity (positive and negative), see INFINITY
 the negative zero, 0.0. It compares equal to the positive zero, but is meaningful in some arithmetic operations, e.g. 1.0/0.0 == INFINITY, but 1.0/0.0 == INFINITY)
 notanumber (NaN), which does not compare equal with anything (including itself). Multiple bit patterns represent NaNs, see nan, NAN. Note that C takes no special notice of signalling NaNs (specified by IEEE754), and treates all NaNs as quiet.
Real floatingpoint numbers may be used with arithmetic operators +  / * and various mathematical functions from math.h. Both builtin operators and library functions may raise floatingpoint exceptions and set errno as described in math_errhandling
Floatingpoint expressions may have greater range and precision than indicated by their types, see FLT_EVAL_METHOD. Assignment, return, and cast force the range and precision to the one associated with the declared type.
Floatingpoint expressions may also be contracted, that is, calculated as if all intermediate values have infinite range and precision, see #pragma STDC FP_CONTRACT.
Some operations on floatingpoint numbers are affected by and modify the state of the floatingpoint environment (most notably, the rounding direction)
Implicit conversions are defined between real floating types and integer, complex, and imaginary types.
See Limits of floating point types and the math.h library for additional details, limits, and properties of the floatingpoint types.
Complex floating typesComplex floating types model the mathematical complex numbers, that is the numbers that can be written as a sum of a real number and a real number multiplied by the imaginary unit: a + bi The three complex types are
Note: as with all type specifiers, any order is permitted: long double complex, complex long double, and even double complex long name the same type. Run this code Output: 1/(1.0+2.0i) = 0.20.4i
Each complex type has the same object representation and alignment requirements as an array of two elements of the corresponding real type (float for float complex, double for double complex, long double for long double complex). The first element of the array holds the real part, and the second element of the array holds the imaginary component. Complex numbers may be used with arithmetic operators +  * and /, possibly mixed with imaginary and real numbers. There are many mathematical functions defined for complex numbers in complex.h. Both builtin operators and library functions may raise floatingpoint exceptions and set errno as described in math_errhandling Increment and decrement are not defined for complex types Relational operators are not defined for complex types (there is no notion of "less than")
In order to support the oneinfinity model of complex number arithmetic, C regards any complex value with at least one infinite part as an infinity even if its other part is a NaN, guarantees that all operators and functions honor basic properties of inifinities and provides cproj to map all infinities to the canonical one (see arithmetic operators for the exact rules) Run this code #include<stdio.h> #include <stdio.h> #include <complex.h> #include <math.h> int main(void) { double complex z = (1 + 0*I) * (INFINITY + I*INFINITY); // textbook formula would give // (1+i0)(∞+i∞) ⇒ (1×∞ – 0×∞) + i(0×∞+1×∞) ⇒ NaN + I*NaN // but C gives a complex infinity printf("%f + i*%f\n", creal(z), cimag(z)); // textbook formula would give // cexp(∞+iNaN) ⇒ exp(∞)×(cis(NaN)) ⇒ NaN + I*NaN // but C gives ±∞+i*nan double complex y = cexp(INFINITY + I*NAN); printf("%f + i*%f\n", creal(y), cimag(y)); } Possible output: inf + i*inf inf + i*nan C also treats multiple infinities so as to preserve directional information where possible, despite the inherent limitations of the Cartesian representation: multiplying the imaginary unit by real infinity gives the correctlysigned imaginary infinity: i × ∞ = i∞. Also, i × (∞ – i∞) = ∞ + i∞ indicates the reasonable quadrant
Imaginary floating typesImaginary floating types model the mathematical imaginary numbers, that is numbers that can be written as a real number multiplied by the imaginary unit: bi The three imaginary types are
Note: as with all type specifiers, any order is permitted: long double imaginary, imaginary long double, and even double imaginary long name the same type. Run this code Output: 1/(3.0i) = 0.3i
Each of the three imaginary types has the same object representation and alignment requirement as its corresponding real type (float for float imaginary, double for double imaginary, long double for long double imaginary). Note: despite that, imaginary types are distinct and not compatible with their corresponding real types, which prohibits aliasing. Imaginary numbers may be used with arithmetic operators +  * and /, possibly mixed with complex and real numbers. There are many mathematical functions defined for imaginary numbers in complex.h. Both builtin operators and library functions may raise floatingpoint exceptions and set errno as described in math_errhandling Increment and decrement are not defined for imaginary types
The imaginary numbers make it possible to express all complex numbers using the natural notation x + I*y (where I is defined as _Imaginary_I). Without imaginary types, certain special complex values cannot be created naturally. For example, if I is defined as _Complex_I, then writing 0.0 + I*INFINITY gives NaN as the real part, and CMPLX(0.0, INFINITY) must be used instead. Same goes for the numbers with the negative zero imaginary component, which are meaningful when working with the library functions with branch cuts, such as csqrt: 1.0  0.0*I results in the positive zero imaginary component if I is defined as _Complex_I and the negative zero imaginary part requires the use of CMPLX or conj. Imaginary types also simplify implementations; multiplication of an imaginary by a complex can be implemented straightforwardly with two multiplications if the imaginary types are supported, instead of four multiplications and two additions. 
(since C99) 
Keywords
char, int, short, long, signed, unsigned, float, double. _Bool, _Complex, _Imaginary
Range of values
The following table provides a reference for the limits of common numeric representations. As the C Standard allows any signed integer representation, the table gives both the minimum guaranteed requirements (which correspond to the limits of one's complement or signandmagnitude) and the limits of the most commonly used implementation, two's complement. All popular data models (including all of ILP32, LP32, LP64, LLP64) use two's complement representation, though.
Type  Size in bits  Format  Value range  

Approximate  Exact  
character  8  signed (one's complement)  127 to 127  
signed (two's complement)  128 to 127  
unsigned  0 to 255  
integral  16  signed (one's complement)  ± 3.27 · 10^{4}  32767 to 32767 
signed (two's complement)  32768 to 32767  
unsigned  0 to 6.55 · 10^{4}  0 to 65535  
32  signed (one's complement)  ± 2.14 · 10^{9}  2,147,483,647 to 2,147,483,647  
signed (two's complement)  2,147,483,648 to 2,147,483,647  
unsigned  0 to 4.29 · 10^{9}  0 to 4,294,967,295  
64  signed (one's complement)  ± 9.22 · 10^{18}  9,223,372,036,854,775,807 to 9,223,372,036,854,775,807  
signed (two's complement)  9,223,372,036,854,775,808 to 9,223,372,036,854,775,807  
unsigned  0 to 1.84 · 10^{19}  0 to 18,446,744,073,709,551,615  
floating point 
32  IEEE754  ± 3.4 · 10^{± 38} (~7 digits) 

64  IEEE754  ± 1.7 · 10^{± 308} (~15 digits) 

Note: actual (as opposed to guaranteed minimal) ranges are available in the library headers <limits.h> and <float.h>
See also
C++ documentation for Fundamental types
