Button presses

const int LED = 13;       // the pin for the LED

const int BUTTON = 7; // the input pin where the  pushbutton is connected

int val = 0;                      // val will be used to store the state  of the input pin

int old_val = 0;               // this variable stores the previous  value of "val"

int state = 0;                   // 0 = LED off and 1 = LED on

void setup() {

 pinMode(LED, OUTPUT); // tell Arduino LED is an output

 pinMode(BUTTON, INPUT); // and BUTTON is an input

}

void loop(){

 val = digitalRead(BUTTON); // read input value and store it

// check if there was a transition

if ((val == HIGH) && (old_val == LOW)){

 state = 1 - state;

}

old_val = val; // val is now old, let's store it

if (state == 1) {

 digitalWrite(LED, HIGH); // turn LED ON

} else {

 digitalWrite(LED, LOW);

}

}

                                                                     EXPLAIN 

We have three variables and initial it to 0 :

int val = 0;

int Old_val = 0;

int state = 0;           

                                                                        LED Turn On

*Press the Button :  

       When we pressed the button val variable  = 1 and old_val variable = 0 it means that

=>state = 1

=>old_val = 1

if(state == 1) 

=>LED turn on.

*Release the Button

      When we released the button val variable = 0, state variable still = 1, and old_val variable = 0.

if(state == 1) 

=> LED turn on.

                               LED turn off                                      

*Press the Button

      When we pressed the button val variable = 1 and we had state = 1 in this case state = 0 and

old_val = 1.

if(state == 0)

=>LED turn off.

*Release the Button

      When we released the button val variable = 0, state variable = 0, and old_val variable = 0.

if(state == 0)

=>LED turn off.