Serial.print Incomplete String?

Projects General Guidance
2

I usually add a count down delay on start to my sketches

  Serial.begin(9600);
  for (int i = 10; i > 0; i--) {
    Serial.println(i);  delay(500);
  }

Then enter data after that. Some boards start as soon as the upload finishes, other restart on the monitor opening.

Also check out my Arduino Software Solutions
for a whole range of solutions to reading text from Serial with the pros and cons of each.
Includes non-blocking reads and non-blocking flushing examples