Interrupts in arduino

int pinTx=12;
volatile int state=HIGH;
void setup()
{
  pinMode(pinTx,OUTPUT);
 attachInterrupt(0,tx,FALLING);
}
void loop()
{
  digitalWrite(pinTx,state);
  if(state==LOW)
  {
    delay(1000);
    digitalWrite(pinTx,HIGH);
  }
  
}
void tx()
{
  state=LOW;
}

int pinTx=12;
volatile int state=HIGH;
void setup()
{
  pinMode(pinTx,OUTPUT);
 attachInterrupt(0,tx,FALLING);
}
void loop()
{
  digitalWrite(pinTx,state);
  if(state==LOW)
  {
    
    digitalWrite(pinTx,state);  // turn off the LED
    delay(1000);		// wait a second
    digitalWrite(pinTx,!state); // invert the state i.e. HIGH
    state=HIGH;                 // again state becomes High
    
  }
  
}
void tx()
{
  state=LOW;
}

int pinTx=12;
volatile int state=HIGH;
void setup()
{
  pinMode(pinTx,OUTPUT);
  digitalWrite(pinTx,state);   // initially turn on the LED
  attachInterrupt(0,tx,FALLING); // this function tells that the interrupt 0 is attached to tx() function and will execute when falling edge is detected
}
void loop()
{
    if(state==LOW)
  {
    digitalWrite(pinTx,state);  // turns off the LED 
    delay(1000);		       // wait a second
    digitalWrite(pinTx,!state); // invert the state i.e. HIGH ..-> this is necessary to turn on the LED again..
    state=!state;                 // and invert the state now state= HIGH you can also write "state=HIGH" or "state=1"
    
  }
  
}
void tx()           // this function will execute every time when you press the button connected to interrupt pin
{
  state=LOW;
}