void setup() {
  Serial.begin(115200);
  float input = 10.4;
  Serial.println((int)input); // 10
  Serial.println((input-int(input))); // 0.40
  Serial.println((input-int(input))*10); //4.00
  Serial.println(int((input-int(input))*10)); // 3 WTF?
  Serial.println((int)((input-(int)input)*10)); // 3 WTF?
  Serial.println(int(round((input-int(input))*10))); // 4 OK
  Serial.println(int(float(4.00))); // 4 OK
}

void loop() {
  // put your main code here, to run repeatedly:

}