float is intended to be a compact native real floating-point type capable of representing a modest range of real numbers. (double is usually a larger and more capable type.) A floating-point constant of type float is suffixed with an f or F.

Various macros in <float.h> describe the capabilities of float. It supports FLT_DIG decimal digits of precision, or FLT_MANT_DIG digits in the native base FLT_RADIX.

float has a range of ±FLT_MAX. The smallest positive non-zero value it can take is FLT_TRUE_MIN, which could be subnormal. The smallest positive normalized value it can take is FLT_MIN.

From C11, if subnormal values are possible, FLT_HAS_SUBNORM expands to 1. If not, it expends to 0. If it is undeterminable, it expands to -1.

FLT_MIN_10_EXP is the lowest integer x that you can give to powf(10.0F, x) and still get a normalized value. FLT_MAX_10_EXP is the highest integer x that you can give to powf(10.0F, x) and still get a normalized value.

FLT_MIN_EXP is the lowest integer x that you can give to powf(FLT_RADIX, x - 1) and still get a normalized value. FLT_MAX_EXP is the highest integer x that you can give to powf(FLT_RADIX, x - 1) and still get a normalized value. FLT_EPSILON is the smallest value you can add to 1.0F to yield something other than 1.0F.

FLT_DECIMAL_DIG is the number of decimal digits that float can retain without rounding error.

From C99, if __STDC_NO_COMPLEX__ is defined, float _Complex is a complex floating-point type that has the same representation as an array of two floats, the first being the real part, and the second the imaginary part, of the complex number it represents. If imaginary is defined in <complex.h>, float _Imaginary is an imaginary floating-point type that has the same representation as a float. float imaginary and float complex are alternative names for these types, available in <complex.h>.

#include <complex.h>
float complex CMPLXF(float re, float im);

The macro CMPLXF expands to a constant expression suitable to initialize a float complex with static or thread-local storage, with a value re + I * im, a complex number with a real component re and an imaginary component im, provided re and im are similarly suitable.

If CMPLXF is unavailable, a portable implementation could be:

#define CMPLXF(RE, IM) \
  (*(float _Complex *) (float[2]) { (RE), (IM) })

This information derives from a comp.std.c thread in May 2009.

A value of type float complex can be split into cartesian co-ordinates with crealf and cimagf, or into polar co-ordinates with cargf and cabsf.