The warrior code is a series of strict laws laid down by StarClan for all of the Clans to follow. While the exact code is not listed anywhere, it is clear to all Clans what the rules in the warrior code are. There are countless other laws in the warrior code. If warriors break this code, a punishment, whether it be from a duty involving caring for the elders to exile to even death, will undoubtedly result. The punishment depends on the severity of the broken code and the Clan leader themself. For example, if an apprentice had been caught eating during a hunting mission, they may be punished simply by not being allowed to take any fresh-kill for the rest of the day. Another example could be if a cat betrayed their Clan. The Clan leader may decide to exile them as proper punishment.
copy from answer.com

FOLLOW THE WARRIOR CODE CLAN CATS

Rule number one is that every cat should defend his/her clan, even at the cost of their life.
Rule number two is that you should not trespass or hunt on another clans territory. If a patrol catches them, they then have permission to chase them off their land.
Rule number three is that kits and elders should be fed first, and, unless they have special permission, aprentices cannot eat until the elders have all been fed.
Rule number four is that prey is not killed for sport. You should not kill anything unless someone plans on eating it. You must also give starclan thanks for its life.
Rule number five says that kits must be six moons old in order to become an apprentice. This rule was famously broken by Brokenstar of Shadowclan, when he forced ShadowClan kits to become apprentices before they were ready. He also trained them too hard, and killed some of them. Some were made warriors before they were even six moons old!
Rule number six says that new warriors must sit a silent vigil, and watch over the camp while the others sleep. They cannot say a word, and must sit outside no matter what the weather is like.
Rule number seven says that a clan cat cannot become the deputy of their clan without having mentored at least one apprentice. this rule was broken when Brambleclaw became deputy because he had never mentored an apprentice when he was named deputy.
Rule number eight says that, should the leader of a clan die or retire, the deputy shall replace the leader.
Rule number nine says that if a deputy dies or retires, the leader must then choose a successor before moonhigh(midnight). this rule was broken when Firestar made Brambleclaw deputy after moonhigh.
Rule number ten says that once every full moon, the clans must have a gathering with each other. Also, there shall be no fighting among them during this time. Also, if they do fight, StarClan sends a cloud to cover the moon, showing they are angry.
Rule eleven says that the clan boundaries must be checked and marked by patrols daily. Also, if a patrol finds a trespassing cat, they must chase him off of their territory.
Rule twelve says no warrior can ever ignore a kit in pain or danger. This rule applies even if the kit is from a different clan. Fireheart and Graystripe saved Mistyfoot's kits from the flood in Fire and ice.
Rule thirteen says that the word of a clan leader is also the Warrior Code.
Rule fourteen says that an honorable cat does not kill in battle, unless the opposing cats are outside the Warrior Code, or if they have to kill in self-defense.
Rule fifteen says that a Warrior rejects the soft life of a kittypet. Cloudpaw broke this rule in the first series by eating kittypet food.