my chicken was choking!!!

[chicken vs duck]

My chicken was choking till my dad had saved him but he had to leave in a hurry or he was going to be late for work. He managed to stop the choking and get most of the food out of its mouth but since hes gone idk what to do and the chicken is still gagging everynow and then and is only slightly less purple

 

[Eggcessive]

It sound like there could be a chunk of food stuck in the throat. Whole corn is not good for chickens, just in case he had that. Is he making any noise when he breathes? He could have a crop problem such as impacted crop or sour crop. Impacted crop should be treated by a vet if at all possible, since they can perform surgery to remove a clump of grass or food stuck. When the grass or food rots, it then can become sour crop, and is much harder to treat successfully. Vomiting a chicken is very very dangerous, and only should be performed by someone who reads how to do it correctly, or the chicken can choke to death. Here are a couple of links to read:
http://www.the-chicken-chick.com/2012/04/answers-from-chicken-vet-on-impacted.html
http://www.tillysnest.com/2012/01/crop-issues.html