bool logtextwrap=false;
unsigned int logtextentry=0;
String logtext [10];

void setup() {
  Serial.begin(115200);                 //seriellen Monitor aktivieren
  Serial.println(F("Start..."));
  delay(100);
}

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

  for (unsigned char i=0; i<255; i++){
    generateLog( ((String)"Log-Eintrag " + i + "\n") );
  }

  Serial.println("Befüllen fertig");
  
  printLog();
}

void generateLog(String text){
  Serial.print((String)"Logtext[" + logtextentry + "]=" +text);
  logtext[logtextentry]=text;
  if (++logtextentry>9){      
    logtextentry =0;
    logtextwrap=true;
  }
}

void printLog(void){
  Serial.println("Ausgabe Log");
  if (logtextwrap){
    for (unsigned char i=logtextentry; i<10; i++){
      Serial.print((String)"Logtext[" + i + "]=" + logtext[i]);
    }
  }
  for (unsigned char i=0; i<logtextentry; i++){
    Serial.print((String)"Logtext[" + i + "]=" + logtext[i]);
  }
  Serial.println("Ausgabe Log fertig");
}