> I thought this was a C 89 requirement too

TIL

It's not a C89 requirement. C89 requires variables to be declared at the top of a block, not a function. So, you could write things like this:

  while (...) {
      int a = 1, b = 2, c = 3;
      printf("%d\n", a + c - b);
  }

Ah okay - I misremembered - I only had to work with strict C89 once and that was close to 15 years ago now, and at a similar time I inherited a codebase that did things the C89 way but it was compiled as C++ so with no enforcement of variables at the top of blocks I didn't really pay attention to where things had been declared when it was first written.

Also from those who learned with Pascal. Traditional Pascal requires that all variables be declared at top of procedure/function in a 'var' section.