Also, although this might be more obvious to people familiar with any C-like language, C++ considers that since 'x' is a character, and its characters are fundamentally just an integer type (maybe a signed 8-bit integer, it depends) the third list is just two constant integers, which are a perfectly reasonable thing to put in a list. Even though that's obviously not what a human sees.

In a language that isn't just pretending to be strongly typed, the compiler would notice that char and whatever-integer-type-42-is aren't the same type, and it would reject your program as nonsense.

But that confusion gets much less chance if the language explicitly distinguishes initialising collections so that "I want N of X" is different from "I want N, and X". Compare Rust's vec! macro:

  let mut v = vec!['x'; 42]; // NOTE semi-colon. Compiles, vector of 42 x characters

  let mut v = vec!['x', 42]; // NOTE comma. Does not compile

  let mut v = vec![b'x', 42]; // NOTE comma. Compiles, vector containing 120 (the ASCII code for 'x') and 42 as bytes

  let mut v = vec![b'x'; 420]; // NOTE semi-colon. Compiles, vector of 420 bytes with value 120

  let mut v = vec![b'x', 420]; // NOTE comma. Does not compile unless you explicitly tell Rust that you mean the low 8-bits of 420 if you do this

I'd actually be enthusiastic about a Clippy warning for the middle one, because it feels like the odds are better than they should be that wasn't what you meant. But on the other hand, the odds of you wanting either possibility are slim, so, not a priority.