The display numbers four positions 0 through 3. Shift 1u left three places to build the mask for position 3, then OR it into the flags already stored. That new bit contributes 8 to the final value.
mask using 1u << 3, OR it into the supplied flags, and print Flags: 10 followed by a newline. Do not replace the calculation with the literal 10.Set mask = 1u << 3, then OR it into flags.