In C, trunc() drops the fraction and moves toward zero. trunc(2.9) is 2, and trunc(-2.9) is -2.
You pass one double. The result is still a double, not an int. Include <math.h>.
Pass the number you want to cut toward zero. Start with this call.
trunc(2.9);| Call | What it does |
|---|---|
trunc(2.9) | Drops the fraction and returns 2. |
Include <math.h>. On GCC, link with -lm. This is not floor(). Floor goes toward negative infinity.
double trunc(double x);
float truncf(float x);
long double truncl(long double x);| Parameter | Description |
|---|---|
| x | Required. The double to cut toward zero. |
| Return Value | Description |
|---|---|
| double | The integer value toward zero, stored as a double. |
Show that both signs move toward zero.
#include <math.h>
#include <stdio.h>
int main(void) {
printf("trunc(3.75) = %.1f\n", trunc(3.75));
printf("trunc(-2.3) = %.1f\n", trunc(-2.3));
printf("trunc(2.5) = %.1f\n", trunc(2.5));
return 0;
}3.75 loses .75 → 3.0.-2.3 becomes -2.0, closer to zero.2.5 truncates to 2.0, not 3.0.-lm.trunc vs floorPositives match; negatives diverge.
#include <math.h>
#include <stdio.h>
int main(void) {
double x = -2.3;
printf("trunc(%.1f) = %.1f\n", x, trunc(x));
printf("floor(%.1f) = %.1f\n", x, floor(x));
printf("ceil(%.1f) = %.1f\n", x, ceil(x));
return 0;
}-2.3 shows the difference clearly.-2.0.-3.0.-2.0 here.Use trunc for the integer part; subtract to get the fraction (or use modf).
#include <math.h>
#include <stdio.h>
int main(void) {
double x = 5.8;
double whole = trunc(x);
double frac = x - whole;
printf("x = %.1f\n", x);
printf("whole = %.1f\n", whole);
printf("frac = %.1f\n", frac);
printf("as int: %d\n", (int)whole);
return 0;
}trunc(5.8) → 5.0.5.8 − 5.0 leaves the fractional part.(int)whole is fine when the value fits in int.modf returns both parts in one call.Browse the full list of C math.h function tutorials.
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