short btn1 = 3;
short btn2 = 2;

short lock = 0;  //defines the button locking veriable

void setup() {
  // put your setup code here, to run once:
Serial.begin(9600);
pinMode(btn1, INPUT_PULLUP);
pinMode(btn2, INPUT_PULLUP);
}

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

if(digitalRead(btn1) == LOW){  //if button 1 is presed
  if(lock != 1){               //if lock is not 1
  //code that is locked in the if statement
    Serial.println("btn1");
    lock = 1;                  //locks this if statement untill lock is not 1
  }
}

if(digitalRead(btn2) == LOW){  //if button 2 is pressed
  if(lock != 2){               //if lock is not 2
  //code that is locked in the if statement
    Serial.println("btn2");
    lock = 2;                  //locks this if statement untill lock is not 2
  }
}
}