Student or Learner
There was a song from the animation movie "Lion King" -
"I just can't wait to be king".
In this sentence I thought it should be like,
"I just can't wait to be a king".
Why was "a" omitted?
Similar sentence is like,
"I am president of the US".
Shouldn't this also be
"I am the president of the US", or "I am a president of the US" ?
The "a" was omitted in the song because in Simba's case, we know which king he wants to be. He wants to take the position of his father. Thus, "I just can't wait to be King" is more natural here.
"I just can't wait to be the King" is also acceptable. The difference between "I just can't wait to be King/be the King" is so subtle that most native speakers wouldn't make a distinction. If we must do so, "to be King" carries a connotation of living in a certain state of being, while "to be the King" carries a connotation of a person filling a role.
It's the same for President. "I am President" and "I am the President" carry very similar meanings -- "I fulfill the role of president," while "I am a president" would be strange in most situations.