Ruby Docs

v3.1.2
Integer
round

How to use

Quick guide

Official content

Returns self rounded to the nearest value with a precision of ndigits decimal digits.

When ndigits is negative, the returned value has at least ndigits.abs trailing zeros:

555.round(-1)      # => 560
555.round(-2)      # => 600
555.round(-3)      # => 1000
-555.round(-2)     # => -600
555.round(-4)      # => 0

Returns self when ndigits is zero or positive.

555.round     # => 555
555.round(1)  # => 555
555.round(50) # => 555

If keyword argument half is given, and self is equidistant from the two candidate values, the rounding is according to the given half value:

:up or nil: round away from zero:

25.round(-1, half: :up)      # => 30
(-25).round(-1, half: :up)   # => -30

:down: round toward zero:

25.round(-1, half: :down)    # => 20
(-25).round(-1, half: :down) # => -20

:even: round toward the candidate whose last nonzero digit is even:

25.round(-1, half: :even)    # => 20
15.round(-1, half: :even)    # => 20
(-25).round(-1, half: :even) # => -20

Raises and exception if the value for half is invalid.

Related: Integer#truncate.

 
               static VALUE
int_round(int argc, VALUE* argv, VALUE num)
{
    int ndigits;
    int mode;
    VALUE nd, opt;

    if (!rb_scan_args(argc, argv, "01:", &nd, &opt)) return num;
    ndigits = NUM2INT(nd);
    mode = rb_num_get_rounding_option(opt);
    if (ndigits >= 0) {
        return num;
    }
    return rb_int_round(num, ndigits, mode);
}

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