Random number

Generating random numbers is a task that comes up a lot while programming. It is often important to know how to do it properly as a lot of languages generate pseudorandom numbers by default.

"Real" random numbers are numbers that are generated with statistical randomness, in contrast to pseudorandom numbers which are generated by using a seed. Supplying the same seed to a pseudorandom number generator would yield the same numbers. In most programming languages, the seed is set to the system's time by default; this will create the illusion of generating statistically random numbers.

Examples[]

C[]

srand(time(0));
int num = rand() % 10; // generates a number from 0 to 9

.NET[]

The System.Random class is used to generate random numbers. Each instance is a separate pseudorandom number generator.

C#[]

Random random = new Random();
random.Next();
random.Next(10); // generates a number from 0 to 9

Visual Basic[]

Dim rand As New Random()
rand.Next(10)

Java[]

Random rand = new Random(System.currentTimeMillis()); //seeding Random with current time
    
// Random integers
int i = rand.nextInt();
int j = rand.nextInt(10); // generates a number from 0 to 9

See Also

Perl[]

int(rand(10)) # generates a number from 0 to 9

PHP[]

rand(0, 9) // generates a number from 0 to 9
mt_rand(0, 9) // like above, but use the MT method

PL/I[]

dcl time builtin;    /* System time HHMISS999 */
dcl random builtin;

dcl number  bin fixed(15);

number = random(time()) * 100 + 1; /* Range 1 - 100 */

Python[]

import random
print random.random()
print random.randrange(10) # generates a number from 0 to 9
print random.randint(0, 9) # generates a number from 0 to 9

Ruby[]

rand(10) # generates a number from 0 to 9

Ada[]

declare
   type Rand_Range is range 0..9;
   package Rand_Int is new Ada.Numerics.Discrete_Random(Rand_Range);
   seed : Rand_Int.Generator;
   Num : Rand_Range;
begin
   Rand_Int.Reset(seed);
   Num := Rand_Int.Random(seed);
   Put_Line(Rand_Range'Image(Num));
end;