Mathematical constants in C provided by math.h

C provides the following mathematical constants in the header file math.h.

C name	Value	Meaning
`M_E`	e	The base of natural logarithms, e.
`M_LOG2E`	log₂e	The base 2 logarithm of e.
`M_LOG10E`	log₁₀e	The base 2 logarithm of e.
`M_LN2`	ln 2	The natural logarithm of 2.
`M_LN10`	ln 10	The natural logarithm of 10.
`M_PI`	π	The circumference of a circle with diameter 1, π.
`M_PI_2`	π/2	Half of π.
`M_PI_4`	π/4	A quarter of π.
`M_1_PI`	1/π	The inverse of π.
`M_2_PI`	2/π	Twice the inverse of π.
`M_2_SQRTPI`	2/(√ π)	The inverse of the square root of π.
`M_SQRT2`	√2	The square root of 2.
`M_SQRT1_2`	1/(√2)	The inverse of the square root of 2.
`HUGE`		The maximum value of a single-precision floating-point number.
`MAXFLOAT`		The maximum value of a non-infinite single-precision floating-point number.
`HUGE_VAL`	∞	Positive infinity.

The following example C program prints out the values of the maths constants.

#include <stdio.h>
#include <math.h>

#define V(x) {x, #x}

struct constant {
    double value;
    const char * name;
} 
constants[] = {
    V(M_E),
    V(M_LOG2E),
    V(M_LOG10E),
    V(M_LN2),
    V(M_LN10),
    V(M_PI),
    V(M_PI_2),
    V(M_PI_4),
    V(M_1_PI),
    V(M_2_PI),
    V(M_2_SQRTPI),
    V(M_SQRT2),
    V(M_SQRT1_2),
    V(HUGE),
    V(MAXFLOAT),
    V(HUGE_VAL),
};

int n_constants = sizeof (constants) / sizeof (struct constant);

int main ()
{

    int i;

    for (i = 0; i < n_constants; i++) {
        printf ("%s: %g\n", constants[i].name, constants[i].value);
    }

    return 0;
}

Download it here.

The output of the example looks like this:

M_E: 2.71828
M_LOG2E: 1.4427
M_LOG10E: 0.434294
M_LN2: 0.693147
M_LN10: 2.30259
M_PI: 3.14159
M_PI_2: 1.5708
M_PI_4: 0.785398
M_1_PI: 0.31831
M_2_PI: 0.63662
M_2_SQRTPI: 1.12838
M_SQRT2: 1.41421
M_SQRT1_2: 0.707107
HUGE: 3.40282e+38
MAXFLOAT: 3.40282e+38
HUGE_VAL: inf

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