// The most scary code you have seen.

void setup() 
{
  Serial.begin(115200);
  
  // dtostrf specifies a MINIMUM size !
  char buffer[20];
  float x = -12345.67890;
  dtostrf( x, 4, 2, buffer);   // it uses 10 bytes of the buffer
  Serial.println(buffer);


  // %d specifies a MINIMUM size !
  char buf[20];
  int i = -12345;
  sprintf(buf, "%4d", i);  // it uses 7 bytes of the buf
  Serial.println(buf);
}

void loop() 
{
}