#define   ARR_SIZE   10
double values[ARR_SIZE];    // float/doubles are the same on AVR8
int index;
int led = 4;
int ledl = 5;
int led3 = 3;
int led6 = 6;
int led7 = 7;
int led10 = 10;
int led8 = 8;

// returns true when a new array of values has been
// received and is ready for further processing.
// Otherwise returns false.
bool check_serial() {
    static bool is_receiving = false;

    while (Serial.available()) {
      digitalWrite(ledl, HIGH);
        String str = Serial.readStringUntil('\n');
        str.trim();

        if (str.length() == 0) {
            digitalWrite(led3, HIGH);

            continue;  // Ignore empty lines.
        }
        else{
          digitalWrite(led10, HIGH);
        }

        if (str == "Start") {
            is_receiving = true;
            index = 0;
            digitalWrite(led6, HIGH);
            continue;
        }
        else{
          digitalWrite(led10, HIGH);
        }

        if (is_receiving) {
            digitalWrite(led, HIGH);
            values[index++] = atof(str.c_str());
            ++index;

            if (index >= 10) {
                digitalWrite(led7, HIGH);
                // We received the final value.
                is_receiving = false;  // Reset the flag.
                index = 0;
                return true;
            }
        }
        else{
          digitalWrite(led10, HIGH);
        }
    }

    return false;
}

void setup() {
    Serial.begin(115200);
    pinMode(led, OUTPUT);
    pinMode(ledl, OUTPUT);
    pinMode(led3, OUTPUT);
    pinMode(led6, OUTPUT);
    pinMode(led7, OUTPUT);
    pinMode(led10, OUTPUT);
    pinMode(led8, OUTPUT);
}



void loop() {
    if (check_serial()) {
        // we received a new array of values. process them all now:
        // ...
    }
    else{
      digitalWrite(led8, HIGH);
    }

    // do other stuff..
}