void testF() {
  float letterX = 2.0;
  float letterY = 7.1;
  float letterZ = 5.7;
  char tempStrX[10];
  char tempStrY[10];
  char tempStrZ[10];
  dtostrf(letterX, 6, 3, tempStrX);
  dtostrf(letterY, 6, 3, tempStrY);
  dtostrf(letterZ, 6, 3, tempStrZ);
  char buf[36];
  sprintf(buf, "The values are %s, %s, and %s.", tempStrX, tempStrY, tempStrZ);
  Serial.println(buf);
}

void setup() {
  Serial.begin(115200);
  // put your setup code here, to run once:
}

void loop() {
  testF();
  delay(100);
}