C Academy · Lesson

Rounding and Absolute Values

floor, ceil, round, fabs.

This lesson covers functions that adjust numbers: floor, ceil, round, and trunc for rounding, plus fabs for absolute value.

They all live in math.h and work with double values.

The floor Function

floor(x) rounds down to the nearest whole number, toward negative infinity.

So floor(3.9) is 3.0, and floor(-1.2) is -2.0.

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

int main(void) {
    printf("%.1f\n", floor(3.9));
    printf("%.1f\n", floor(-1.2));
    return 0;
}