instance method

Kernel#rand

(?0) -> ::Float

(::int arg0) -> ::Integer

(::Range[::Integer] arg0) -> ::Integer?

(::Range[::Float] arg0) -> ::Float?

rand(max=0) → number

static VALUE
rb_f_rand(int argc, VALUE *argv, VALUE obj)
{
    VALUE vmax;
    rb_random_t *rnd = default_rand_start();

    if (rb_check_arity(argc, 0, 1) && !NIL_P(vmax = argv[0])) {
        VALUE v = rand_range(obj, rnd, vmax);
        if (v != Qfalse) return v;
        vmax = rb_to_int(vmax);
        if (vmax != INT2FIX(0)) {
            v = rand_int(obj, rnd, vmax, 0);
            if (!NIL_P(v)) return v;
        }
    }
    return DBL2NUM(random_real(obj, rnd, TRUE));
}

If called without an argument, or if max.to_i.abs == 0, rand returns a pseudo-random floating point number between 0.0 and 1.0, including 0.0 and excluding 1.0.

Example

rand        #=> 0.2725926052826416

When max.abs is greater than or equal to 1, rand returns a pseudo-random integer greater than or equal to 0 and less than max.to_i.abs.

Example

rand(100)   #=> 12

When max is a Range, rand returns a random number where range.member?(number) == true.

Negative or floating point values for max are allowed, but may give surprising results.

Example

rand(-100) # => 87
rand(-0.5) # => 0.8130921818028143
rand(1.9)  # equivalent to rand(1), which is always 0

Kernel.srand may be used to ensure that sequences of random numbers are reproducible between different runs of a program.

Related: Random.rand.

Example

rand(100.0)        # => 64 (Integer because max.to_i is 100)
Random.rand(100.0) # => 30.315320967824523

Ruby version changes

3.0
- Random::DEFAULT is deprecated since its value is now confusing and it is no longer global, use Kernel.rand/Random.rand directly, or create a Random instance with Random.new instead. [Feature #17351]

See also #raise #Rational #puts #readline also in 4.1 · 3.4 · 3.3 · 3.2 · 3.1 · 3.0

‹ prev#raise next ›#Rational