How can you tell if a hexadecimal number is negative (in two's complement)?

Look at the leading hex digit: 0–7 means positive, 8–F means negative (its top bit — the sign bit — is 1).

For 32-bit integers:

0x7FFFFFFF = +2,147,483,647 (positive, starts with 7)
0x80000000 = -2,147,483,648 (negative, starts with 8)
0xFFFFFFFF = -1             (negative, starts with F)
0x00000001 = +1             (positive, starts with 0)

Why 8-F means negative:

• Hex digit 8 = binary 1000
• The leading 1 is the sign bit
• Hex digits 0-7 start with binary 0xxx (positive)
• Hex digits 8-F start with binary 1xxx (negative)

Quick reference:

Common values to recognize:

• 0xFFFFFFFF = -1
• 0xFFFFFFFE = -2
• 0x80000000 = INT_MIN (most negative)
• 0x7FFFFFFF = INT_MAX (most positive)

Tip: When debugging, seeing 0xFFFF... usually means -1 or an error code, not a huge positive number!