I thought these issues are obvious by now.

Some typical points to consider:

1) Never store a length as an int, unsigned, long, etc. Use size_t (or ssize_t) instead.

2) Never store a pointer as an int, unsigned, long, etc. Use uintptr_t (or intptr_t). ptrdiff_t is the type to use for pointer differencing.

3) When comparing or casting to a signed type, watch out for sign extension. For example (short) -1 (0xffff) becomes 2^32-1 (0xffffffff) when casted to uint32_t. Remember char is usually a signed type.

4) Some legacy library functions return int, which is a signed 32-bit value in Windows and Linux (remember point 3). Watch out for these cases. For example don't use ftell and check s[n]printf return value.