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# wandrson/RandomCardDraw.pde Last active Aug 29, 2015

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The following example demonstrates how to produce the numbers 1 to X in a random order, where each number only appears once, and that all numbers are produced.
 // FILE: RandomCardDraw.ino // AUTHOR: Rob Tillaart and Walter Anderson // VERSION: 1.0.0 // PURPOSE: generate random sequence (optimized) // DATE: April 24, 2014 // URL: // The Entropy library provides true random numbers and can be obtained from: // http://code.google.com/p/avr-hardware-random-number-generation/wiki/WikiAVRentropy #include const byte MAX_VALUE=10; int RandomDraw[MAX_VALUE+1]; byte tmp; // The following function swaps the contents of an array at the locations a & b void swap(int a, int b) { int t = RandomDraw[a]; RandomDraw[a] = RandomDraw[b]; RandomDraw[b] = t; } void setup() { Serial.begin(9600); // Initialize array with the sequence of values we will randomly draw from for (int i=0; i<=MAX_VALUE; i++) { RandomDraw[i] = i; } // Initialize the Entropy library to ensure that the draws are truely random. Entropy.Initialize(); Serial.print("Starting to draw random sequences from 1 to "); Serial.println(MAX_VALUE); } void loop() { // fetch MAX_VALUE random numbers from the sequence 1 .. MAX_VALUE with no repeats and no missed values for (int i=1; i<=MAX_VALUE; ++i) { tmp = Entropy.random(1, (MAX_VALUE+1)-i); // select from a decreasing set Serial.print(RandomDraw[tmp]); if (i < MAX_VALUE) Serial.print(","); swap(tmp, (MAX_VALUE+1)-i); // switch the chosen one with the last of the selection set. } Serial.println(" "); }