I have this code and I happen to two problems.

I want to do that when you click once to jump, not when held down.

Code:
// Saltar
  	posicion = c_trace(me,vector(me.x, me.y, -1100),IGNORE_ME); 
if (key_space == 1 && posicion >= 0){
contador += time_step/16;
var velocidadsalto = (10) - (18*contador);
c_move(me, vector(0,0,velocidadsalto), NULL, GLIDE);
} else {
contador = 0;
c_move(me, vector(0,0,-10), NULL, GLIDE);
}


Then I would like to know how I can detect that I do a double jump. ie double key_space