[GM] changing graphics while running

i'v seen that in other people's games, the player changes graphics while running.
can someone tell me how to do this?

Absolutely, but you'll need to better outline what it is exactly. Do you mean running as opposed to walking, or running as in basic movement in a given direction?

running as in basic movement in a given direction? (as opposed to standing still)

Ah, thats simple enough. Make it so when a movement key is pressed (not held, pressed) the sprite is changed accordingly. When it is released, change it back.

oh! i overlooked that. i didnt think it was so simple. thanks man!

[edit]
wait, that's not what i meant. i dont want a running sprite. i want a running sprite animation.
in other words:
i want my character to move his legs (like in the legend of zelda platformer)

can you tell me how to do that?

Just move his legs and have no motion? Then remove the motion...

thats not what i mean. i want him to move his legs and have motion. i have heard something about subimages but im not completely sure what they are. what are they?

Look through the sticky full of examples I stopped updating for some reason. In there you should find one called FoxNL's Platform example. (or whatever it's called, I know it had Fox somewhere in it) That should answer all of your questions.

EDIT: http://rmrk.net/index.php/topic,12923.0.html

ok, thanks! but i have one more question.
can someone give me the expressions (that can be used in the "Test Experssion" event) that:

-test weather the player is moving left
-test weather the player is moving right
-test weather the player is not moving to the left or right (but might be moving up or down)
-test weather the player is in the air

-hspeed<0
-hspeed>0
-hspeed=0
-place_free(x,y+2)

wow! you're either an expert game maker, or im a newb game maker (which i am)..... or both..... lol! thanks!

lol, not quite expert I don't think, I still ask a dumb question or two myself every now and then. That wasn't a dumb question though, it's good you asked it. So you know, you can use basic math symbols, like +, -, *, (multiplication) or / (division) in almost any kind of mathematic formula in GM. For instance, if you wanted to make an object move at half the player's current hspeed, you would say:

self.hspeed=player.hspeed/2