Comparing "changchang" and "jingchang"
Both 常常 (chángcháng) and 经常 (jīngcháng) are adverbs expressing the idea of "often," though their usage differs in some small details.
Used as an Adverb
常常 and 经常 both can be used to express frequency, meaning "often," and that the time between each instance it happens is very short. In this case, they are interchangeable.
常常 / 经常 + Verb
- 我 常常 收到 垃圾 短信 。I often receive junk texts.
- 你们 经常 加班 吗 ？Do you guys often work overtime?
- 他们 常常 吵架 。They often argue.
Neither 常常 nor 经常 can't be placed before the subject:
- 常常 他 不 吃 早饭 。
- 经常 他 不 吃 早饭 。
- 他 经常 不 吃 早饭 。He often skips breakfast.
Note that 常 (by itself) is used for future frequent actions in colloquial Chinese.
- 常 来 玩 ！Come and hang out often!
- 常 联系 ！Let's keep in touch!
Used as an Adjective
Although not so commonly used in this way, 经常 can also be used as an adjective referring to things that happens very frequently. 常常 can't be used this way.
A simple example:
- 她 忘 带 钥匙 是 经常 的 事情 。It's a regular thing for her to forget to bring her keys.
经常 and 常常 can share the same negative form 不常. You can also simply use 不 to negate both 经常 and 常常, although 不常常 is not super common.
A few examples:
- 他 不 常 抽烟 。He doesn't smoke very often.
- 我 妈妈 不 经常 网购 。My mother doesn't often shop online.