source code:

var rightKeyIsDown:Boolean = false;
var leftKeyIsDown:Boolean = false;
var upKeyIsDown:Boolean = false;
var downKeyIsDown:Boolean = false;

var gravity:Number = 5;
var yVelocity:Number = 0;
var canJump:Boolean = false;

stage.addEventListener(KeyboardEvent.KEY_DOWN, PressAKey);
stage.addEventListener(KeyboardEvent.KEY_UP, ReleaseAKey);

function PressAKey(event:KeyboardEvent):void
{
if(event.keyCode == Keyboard.RIGHT)
{
rightKeyIsDown = true;
}
if(event.keyCode == Keyboard.LEFT)
{
leftKeyIsDown = true;
}
if(event.keyCode == Keyboard.UP)
{
upKeyIsDown = true;
}
if(event.keyCode == Keyboard.DOWN)
{
downKeyIsDown = true;
}
}

function ReleaseAKey(event:KeyboardEvent):void
{
if(event.keyCode == Keyboard.RIGHT)
{
rightKeyIsDown = false;
}
if(event.keyCode == Keyboard.LEFT)
{
leftKeyIsDown = false;
}
if(event.keyCode == Keyboard.UP)
{
upKeyIsDown = false;
}
if(event.keyCode == Keyboard.DOWN)
{
downKeyIsDown = false;
}
}

cricle_mc.addEventListener(Event.ENTER_FRAME, moveCricle);

function moveCricle(event:Event):void
{
if(rightKeyIsDown)
{
cricle_mc.x += 5;
}
if(leftKeyIsDown)
{
cricle_mc.x -= 5;
}
if(upKeyIsDown && canJump)
{
yVelocity = -30;
canJump = false;
}
yVelocity += gravity;
if(!floor_mc.hitTestPoint(cricle_mc.x, cricle_mc.y, true))
{
cricle_mc.y += yVelocity;
}
if(yVelocity > 40)
{
yVelocity = 40;
}
for(var i:int = 0; i<10; i++)
{
if(floor_mc.hitTestPoint(cricle_mc.x, cricle_mc.y, true))
  {
  cricle_mc.y--;
  yVelocity = 0;
  canJump = true;
  }
}
}