if(key_z)
{
//What do I write here to stop the button works????????
}

if(key_a)
{
//What do I write here to stop the button works???????
}

if(key_d)
{
//What do I write here to stop the button works???????????
}

if(key_s)
{
//What do I write here to stop the button works?????????
}

}