Random number in array

Projects Programming
3

agree with @anon57585045, since you have all the numbers between 0 and SIZE-1 in your array of size SIZE, the simplest way that will lead to guaranteed timing is to fill the array in sequential order and then shuffle.

There is a well know shuffle algorithm called the Fisher–Yates shuffle

try this:

const int SIZE = 10;
int array[SIZE] ;

// Fisher–Yates shuffle
template<typename T>
void shuffleArray(T* a, const size_t size) {
  for (size_t i = size - 1; i > 0; --i) {
    size_t r = random(0, i + 1); // generate rand numbers from 0 to i
    T tmpSwap = a[i];
    a[i] = a[r];
    a[r] = tmpSwap;
  }
}

void printArray(const int* a, const size_t size) {
  for (size_t i = 0; i < size; i++) {
    Serial.print(a[i]); Serial.write(' ');
  }
  Serial.println();
}

void setup() {
  Serial.begin(115200); Serial.println();

  // randomize
  randomSeed(analogRead(A0));

  // fill the array in sequential order
  for (int i = 0; i < SIZE; i++) array[i] = i;
  printArray(array, SIZE);

  // shuffle the array
  shuffleArray(array, SIZE);
  printArray(array, SIZE);
}

void loop() {}

or if template is intimidating

const int SIZE = 10;
int array[SIZE] ;

// Fisher–Yates shuffle
void shuffleArray(int* a, const size_t size) {
  for (size_t i = size - 1; i > 0; --i) {
    size_t r = random(0, i + 1); // generate rand numbers from 0 to i
    int tmpSwap = a[i];
    a[i] = a[r];
    a[r] = tmpSwap;
  }
}

void printArray(const int* a, const size_t size) {
  for (size_t i = 0; i < size; i++) {
    Serial.print(a[i]); Serial.write(' ');
  }
  Serial.println();
}

void setup() {
  Serial.begin(115200); Serial.println();

  // randomize
  randomSeed(analogRead(A0));

  // fill the array in sequential order
  for (int i = 0; i < SIZE; i++) array[i] = i;
  printArray(array, SIZE);

  // shuffle the array
  shuffleArray(array, SIZE);
  printArray(array, SIZE);
}

void loop() {}