Function	Description	Example
`double floor(double x)`	Round down (largest integer ≤ x)	`floor(3.8) → 3`
`double ceil(double x)`	Round up (smallest integer ≥ x)	`ceil(3.2) → 4`
`double round(double x)`	Round to nearest integer	`round(3.5) → 4`
`double trunc(double x)`	Truncate (remove fractional part)	`trunc(-3.8) → -3`

Key differences:

Function	Description
`double modf(double x, double *intpart)`	Splits x into integer and fractional parts
`double frexp(double x, int *exp)`	Splits x into mantissa and exponent
`double ldexp(double mantissa, int exp)`	Computes `mantissa × 2^exp`

Example using modf:

double ip; double fp = modf(3.14, &ip); /* ip = 3, fp = 0.14 */

Function	Description
`double sin(double x)`	Sine
`double cos(double x)`	Cosine
`double tan(double x)`	Tangent
`double asin(double x)`	Arcsine
`double acos(double x)`	Arccosine
`double atan(double x)`	Arctangent
`double atan2(double y, double x)`	Arctangent with quadrant awareness

All angles are in radians, not degrees.

Quick Knowledge Points

<math.h> functions work on double by default.
For float, use versions like sinf, cosf, fabsf, etc.
On Linux/Mac, you must link the math library:
gcc file.c -lm
To split a number into integer & fractional parts, prefer modf() instead of writing your own function.