Minimum inputs for a full-adder How many input signals must a full-adder have to perform one-bit addition with carry?

Introduction / Context:
The full-adder is the standard one-bit arithmetic building block in digital systems. It extends the half-adder by including carry propagation, enabling multi-bit addition via cascading. Recognizing its inputs is essential for correct interfacing and timing analysis.

Given Data / Assumptions:

• Signals involved: operand bit A, operand bit B, and carry-in Cin.
• Outputs: Sum and carry-out Cout.

Concept / Approach:
A full-adder must account for two operand bits and an incoming carry from a less significant stage. Therefore it needs exactly three inputs. Any additional inputs would imply extra operands or control not part of the canonical full-adder definition.

Step-by-Step Solution:
Identify operands: A and B.Account for carry chain: Cin.Count inputs: 3 total.

Verification / Alternative check:
Standard truth tables for a full-adder show 2^3 = 8 rows, confirming three inputs (A, B, Cin).

Why Other Options Are Wrong:

• 2: That is a half-adder (no carry-in).
• 4 or 5: Would represent nonstandard or extended adders (e.g., with extra operands or control), not the basic full-adder.

Common Pitfalls:

• Confusing the full-adder with a half-adder.
• Miscounting Cin as an output rather than an input.

Final Answer:
3