float pi=3.141592;
char pi_str[5];
char serialMsgBuf[128];

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
  dtostrf(pi,4,2,pi_str);

  sprintf(serialMsgBuf,    "pi_str: %s", pi_str);
       
  Serial.println(serialMsgBuf);
  delay(100);
}