how can i solve this should

how can i solve this should be keys (5 or 10 keys if possible 10) of both letters and numbers.
here (about 5 num :confused: bers and letters long)
here I want to make an nfc locker later

int keys[] = {"key1", "key2", "key3", "key4", "key5"};
byte count = sizeof(keys);

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
   for (byte i=0; i <= sizeof(keys); i++){
      Serial.println(i);
      Serial.println(keys);
           
    }
 

}

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

}