How do I use the character 当, pronounced as a 4th tone? When pronounced as a 4th tone, this character has the meaning "to think/regard as/replace, suitable/adequate, at or in the very same". It's the first meaning I'm interested in. My dictionary gives the example sentence


  你当我不知道吗？ Do you think I've no idea?


The problem is, I can't find any more example sentences or articles or information on how to use this or when it's suitable to use it, because 当 pronounced as a 1st tone is more common and all my search results are for that pronunciation. 

So my questions are - can anyone provide me some examples of how to use this character (4th tone)? And can anyone explain when to use it? (what is the difference between 你当我不知道吗 and 你以为我不知道?)

Thanks in advance!
According to《规范》one of the meanings of 


  当 
  
  dàng


is


  以为


and they give the sample sentence:


  我当你不来了呢


So it seems the difference between 当 and 以为 is minimal at best.



As for other example sentences, here's a gloss of the PLC dictionary provided by Pleco:


  ADJECTIVE
  
  1 proper; right; appropriate
  
  以上意见当否, 请批示。 
  Yǐshàng yìjian dàng fǒu, qǐng pīshì.
  We are awaiting your comment on the proposals set forth above. 
  
  2 that very (day, etc.)
  
  当李的产量 
  dàng lǐ de chǎnliàng
  the output of that season 
  
  3 of the same; of one's own
  
  当村的小伙伴们 
  dàng cūn de xiǎo huǒbàn men
  little friends of one's village 
  
  VERB
  
  1 match; be equal to
  
  他一个人能当两个人用。 
  Tā yī ge rén néng dàng liǎng ge rén yòng.
  He can do the work of two persons put together. 
  
  2 treat as; regard as; take for
  
  不要把支流当主流。 
  Bùyào bǎ zhīliú dàng zhǔliú.
  Don’t take minor aspects for major ones. 
  
  3 think
  
  我当你不知道呢。 
  wǒ dàng nǐ bùzhīdào ne.
  Well, I thought you didn’t know. 
  
  4 pawn
  
  当衣服 
  Dàng yīfu
  pawn one’s clothes; put one’s clothes in pawn 


Hopefully that gives you a better idea of how it's used.