/*
  Forum: https://forum.arduino.cc/t/method-to-print-fixed-point-values/82093/3
  Wokwi: https://wokwi.com/projects/388290041518382081
*/

void setup() {
  Serial.begin(115200);
  printFixedDec(-1003,0);
  Serial.println(" mm");
  printFixedDec(-1003,1);
  Serial.println(" cm");
  printFixedDec(-1003,3);
  Serial.println(" m");
  printFixedDec(-1003,6);
  Serial.println(" km");
}

void loop() {
}


void printFixedDec( long val, int dotPosition)  // we don't need no loops ...
{
  String zeros = "0000000000";
  String out = "";
  char sign = ' ';
  if(val < 0 ){
    val = -val;
    sign = '-';
  };
   out = String(val);
  if (dotPosition > 0) {
    int len = out.length();
    if (len < dotPosition) {
      out = zeros.substring(0,dotPosition-len+1)+out;
      len = out.length();
    }
    out = out.substring(0,len-dotPosition)+"."+ out.substring(len-dotPosition);
  } 
  Serial.print( sign+out );  
}