CareerCup

a2i is the string to integer in c:
- overflow depending on integer size of that machine, e.g. max and min of integer
- two "--" like "--1234"
- "123-32"
- decimal "." or "," or "..", or ",,"
- thousand seperators, depending on cultural settings (e.g. . or ' ...)
- what surounds the integer, spaces, end of string, other characters like "124zoo"
- whitespaces at the beginning, which of them
- only base 10, or octal, binary, hex with suffix, prefix
- white spaces, like line breaks, back spaces in between
- encodings, like utf8 etc...
- special characters like chinese, japanese (ichi, ni, etc..)
...

You missed "-" "+" (+1 is OK but + is not integer)

Most of the cases you raised are correct except they are of the same pattern (i.e. none [0-9] after first char)

The interviewer was pretty peculiar about NULL vs. empty string. I said check input in the beginning but he dismissed NULL outright ("that is an application level error"). Then reminded me of checking empty string.