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Division of integers in C rounds the result to an integer. The result is always rounded towards zero.

16 / 3 ⇒ 5 -16 / 3 ⇒ -5 16 / -3 ⇒ -5 -16 / -3 ⇒ 5

To get the corresponding remainder, use the ‘`%`’ operator:

16 % 3 ⇒ 1 -16 % 3 ⇒ -1 16 % -3 ⇒ 1 -16 % -3 ⇒ -1

‘`%`’ has the same operator precedence as ‘`/`’ and ‘`*`’.

From the rounded quotient and the remainder, you can reconstruct the dividend, like this:

int original_dividend (int divisor, int quotient, int remainder) { return divisor * quotient + remainder; }

To do unrounded division, use floating point. If only one operand is
floating point, ‘`/`’ converts the other operand to floating
point.

16.0 / 3 ⇒ 5.333333333333333 16 / 3.0 ⇒ 5.333333333333333 16.0 / 3.0 ⇒ 5.333333333333333 16 / 3 ⇒ 5

The remainder operator ‘`%`’ is not allowed for floating-point
operands, because it is not needed. The concept of remainder makes
sense for integers because the result of division of integers has to
be an integer. For floating point, the result of division is a
floating-point number, in other words a fraction, which will differ
from the exact result only by a very small amount.

There are functions in the standard C library to calculate remainders from integral-values division of floating-point numbers. See The GNU C Library in The GNU C Library Reference Manual.

Integer division overflows in one specific case: dividing the smallest
negative value for the data type (see Maximum and Minimum Values)
by -1. That’s because the correct result, which is the
corresponding positive number, does not fit (see Integer Overflow)
in the same number of bits. On some computers now in use, this always
causes a signal `SIGFPE`

(see Signals), the same behavior
that the option `-ftrapv` specifies (see Signed Overflow).

Division by zero leads to unpredictable results—depending on the
type of computer, it might cause a signal `SIGFPE`

, or it might
produce a numeric result.

**Watch out:** Make sure the program does not divide by zero. If
you can’t prove that the divisor is not zero, test whether it is zero,
and skip the division if so.

Next: Numeric Comparisons, Previous: Mixed Mode, Up: Arithmetic [Contents][Index]