How can I randomly generate one of two states, with the probability of 'red' being generated 10% of the time, and 'green' being generated 90% of the time?
Every 2 second either a green or a red light will blink.
This sequence will continue for 5 minutes.
The total number of occurrences of a blinking light should be 300.
Random.NextDouble returns a number between 0 and 1, so the following should work:
if (random.NextDouble() < 0.90) { BlinkGreen(); } else { BlinkRed(); } 
Either
Random rg = new Random(); int n = rg.Next(10); if(n == 0) { // blink red } else { // blink green } or
Random rg = new Random(); double value = rg.NextDouble(); if(value < 0.1) { // blink red } else { // blink green } This works because Random.Next(int maxValue) returns a uniformly distributed integer in [0, maxValue) and Random.NextDouble returns a uniformly distributed double in [0, 1).
[0, maxValue) is a ')' and not a ']'. This means that the extreme value (maxValue) is not included in the range. Thus, [0, maxValue) = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}.public class NewRandom { private static Random _rnd = new Random(); public static bool PercentChance(int percent) { double d = (double)percent / 100.0; return (_rnd.NextDouble() <= d); } } To use:
if (NewRandom.PercentChance(10)) { // blink red } else { // blink green } The other answers will definitely work if you need a random distribution that favors 90% green.
However, if you need a precise distribution, something like this will work:
void Main() { Light[] lights = new Light[300]; int i=0; Random rand = new Random(); while(i<270) { int tryIndex = rand.Next(300); if(lights[tryIndex] == Light.NotSet) { lights[tryIndex] = Light.Green; i++; } } for(i=0;i<300;i++) { if(lights[i] == Light.NotSet) { lights[i] = Light.Red; } } //iterate over lights and do what you will } enum Light { NotSet, Green, Red } 
while (i < 30) and you set the value to Light.Red. </nitpicking>Building on Michaels answer, but adding further context from the question:
public static void PerformBlinks() { var random = new Random(); for (int i = 0; i < 300; i++) { if (random.Next(10) == 0) { BlinkGreen(); } else { BlinkRed(); } // Pause the thread for 2 seconds. Thread.Sleep(2000); } } 
I'm guessing you have the timing part down (so this code doesn't address that). Assuming "nice" division, this will generate 10% reds and 90% greens. If the exactness isn't important, Michael's answer already has my vote.
static void Main(string[] args) { int blinkCount = 300, redPercent = 10, greenPercent = 90; List<BlinkObject> blinks = new List<BlinkObject>(300); for (int i = 0; i < (blinkCount * redPercent / 100); i++) { blinks.Add(new BlinkObject("red")); } for (int i = 0; i < (blinkCount * greenPercent / 100); i++) { blinks.Add(new BlinkObject("green")); } blinks.Sort(); foreach (BlinkObject b in blinks) { Console.WriteLine(b); } } class BlinkObject : IComparable<BlinkObject> { object Color { get; set; } Guid Order { get; set; } public BlinkObject(object color) { Color = color; Order = Guid.NewGuid(); } public int CompareTo(BlinkObject obj) { return Order.CompareTo(obj.Order); } public override string ToString() { return Color.ToString(); } } 
var random = new Random(); for (var i = 0; i < 150; ++i) { var red = random.Next(10) == 0; if (red) // .. else // Green } random.Next(10) will randomly return the numbers 0..9 and there is 10% chance of it returning 0.
If you want these just to look random, you might want to implement shuffle bag
http://web.archive.org/web/20111203113141/http://kaioa.com:80/node/53
and
Need for predictable random generator
This way the blinking period should look more natural and you can simply implement the restricted number of blinks.
