In Chinese,zero in the year, O or Ling?
I noticed that in the introduction for the dates in the Chinese course the example says to use Ling (0) for zero when saying the year. But in the course you use O and nothing is said. What is the reason for this? thx.
I am a native speaker from Taiwan. The symbol 〇 (not "0") is used in print, for example, in contacts, flyers, and calendars to express the year. It has to be 二〇一八 although some people tend to replace the round zero with the thin numeric 0. You can use either 2018 or 二〇一八. The combination 二零一八 is very rare. I have seen similar use in movie titles, but not in other contexts.
There's no single answer to this. There are basically three major systems in use, and three minor ones.
The most common is actually "Arabic" numerals as used in English. These are used pretty universally, for everything from ATM machines to road signs and mailing addresses. Most people use these when they write, though it is worth noting that the way these numbers are written in Chinese handwriting can sometimes be confusing for a second or two. Thus, most dates would be written "2018" in most formats.
Another every common form is to use a hybrid of Arabic and Chinese numerals. This is especially common when dealing with large numbers. For instance, the population of China is 1.4 billion. In Chinese this would most frequently be written 14亿 with 亿 meaning 100 million. This hybrid system is also sort of what you see when you see the year written 二OO八 - the character is clearly taken from western 0, though in simplified Chinese, O is actually supposed to be the correct character. This is most often used in numbers that would be read individually in a sequence rather than as a single number （二OO八 “er ling ling ba" instead of 两千零百零八). O is also used on signage, or in places where the character 零 might be hard to read.
The third method is to use all Chinese numbers. This is the most cultural and traditional way to do things. Thus Chinese numbers will be used on things that people want to give an air of formality to, or to be more culturally evocative. Thus 零 is what you would use in calligraphy. Similarly, while street signs tend to use Arabic numerals, actual street names usually use Chinese numbers. Thus Beijing's Third Ring Road is called 三环 while a sign saying that the third ring road will be in three kilometers might just say "三环 3km." You can use Chinese numbers for basically everything. I did when I was a student, mostly to make sure I learned them, and because I thought they were cool. My friends thought I was a pain in the ass, though, and the post office once rolled their eyes at me and told me to at least write the Chinese "zip code" in arabic numbers. Another way to think of this is that when you are using numbers to count, or enter an integer value, or anything that you might be tempted to use in a calculator, use arabic values, whereas if you are transcribing speech, or other linguistic uses of numbers, you would usually write them out.
Another system that you will see is the financial system. This is a very old system of writing numbers in very complex ways to complicate forgery. It was also used on formal imperial documents. Today, you'll see it on coins and paper money. In this case the numbers are pronounced the same, but written 壹 贰 叁 肆 伍 陆 柒 捌 玖， while for the orders of magnitude ten is 拾, hundred is 佰， thousand is 仟, ten thousand is 萬, and hundred million is 億. Technically, in the PRC, 零 is part of the "Financial" numbering system, whereas 〇 is part of the "normal" system, however people still use 零 more often than the other financial numbers.
Another minor system you'll see are the "Heavenly Stems." This has its origins in the complex math of the Chinese traditional calendar's sexagenary cycle. But it's most commonly used today like we would use "A. B. C." for outlining. In this system, the numbers go 甲 (jia) 乙 (yi) 丙 (bing) 丁 (ding) 戊 (wu) 己 (ji) 庚 (geng) 辛 (xin) 壬 (ren) 癸 (gui). These are used in numbering lots of things, including train cars, seating sections in movie theaters, building entrances, classes of students, etc. They are also used in astrology and fenghsui.
The last minor system is really a collection of various colloquial terms that can be used to replace numbers for greater verbal clarity, or simply as part of a local accent. Some of these are universal, and are also used by the Chinese military in radio operations, others are dialect. These are pronounced differently, and seldom seen written, but have their own characters. So for 1 they say "yao" 幺, for two, before a classifier, or in larger numbers, you say "liang" 两 (this one often is written, because it would be incorrect to say 二条路, for example, which would sound like "No. 2 Tiao Road," rather than "two roads"). In the Dongbei accent they tend to drop the final nasalizations (for example 什么 "shenme" in Dongbei is said 啥 "sha" as in "啥意思？" for 什么意思 meaning "what's your point?") so they pronunce "san" as "sa" which is written 仨. In military radio communications zero is 洞. In Classical Chinese there were also words for 20 (廿 nian) 30 (卅 sa) which you will see in place names, and maybe in Cantonese.