int button_Minus  =  8;
int button_Plus   =  9;
int button_Select = 10;

float x;
float y=10;
float z=10;

bool buttonState1;                                 // current state of the button
bool lastButtonState1;                             // previous state of the button
bool buttonState2;                                 // current state of the button
bool lastButtonState2;                             // previous state of the button
bool buttonState3;                                 // current state of the button
bool lastButtonState3;                             // previous state of the button

unsigned long  prevmillis;                         // to replace delay(50)
unsigned long  timeButtonSelectLOW;                // to calculate 2 seconds



void setup() {
  pinMode(button_Minus, INPUT_PULLUP);
  pinMode(button_Plus,  INPUT_PULLUP);
  pinMode(button_Select,INPUT_PULLUP);
  Serial.begin(115200);                                      //
  Serial.println(F("go ! press a button"));   
}



void loop(){
 
  
  unsigned long now = millis();                // to replace delay(50)    
  if (now - prevmillis > 20) {                 // 20 ms (instead of 50)
    prevmillis = now;  



    // option 1
    buttonState1 = digitalRead(button_Minus);
    if (buttonState1 != lastButtonState1) {
      lastButtonState1 = buttonState1;  
      
      if (buttonState1 == LOW) { 
        y=y-0.1;
        Serial.println(F("button_Minus")); 
      }  
    }
    


    // option 2
    buttonState2 = digitalRead(button_Plus);
    if (buttonState2 != lastButtonState2) {
      lastButtonState2 = buttonState2;
      if (buttonState2 == LOW) { 
        z=z+0.1;
        Serial.println(F("button_Plus"));       
      }  
    }
 



    // option 3   
    buttonState3 = digitalRead(button_Select);
    if (buttonState3 != lastButtonState3) { 
      lastButtonState3 = buttonState3;

      if (buttonState3 == LOW) {
        Serial.println(F("button_Select"));          
      } 
    }
  }
}