#define ArrLen(x)        (sizeof(x)/sizeof(x[0]))

struct Node {
    uint8_t first, last;
    void *next[];
};

struct Node node_A = { 'A','B', nullptr };
struct Node node_B = { 'B','C', nullptr };
struct Node node_C = { 'C','D', nullptr };

struct Node node_start = {
    .first = 'E',
    .last  = 'F',
    .next = {
        &node_A,
        &node_B,
        &node_C,
    }
};

void setup() {
  Serial.begin(9600);
  for (int i = 0; i<3; i++)
    Serial.print(i),
    Serial.print(" "),
    Serial.println(node_start.next[i].first);
}

void loop() {
  // put your main code here, to run repeatedly:

}