Flight attendant. Flight attendants or cabin crew (also known as stewards/stewardesses, air hosts/hostesses, cabin attendants) are members of an aircrew employed by airlines primarily to ensure the safety and comfort of passengers aboard commercial flights, on select business jet aircraft, and on some military aircraft.
Half adder circuit. To understand what is a half adder you need to know what is an adder first. Adder circuit is a combinational digital circuit that is used for adding two numbers. A typical adder circuit produces a sum bit (denoted by S) and a carry bit (denoted by C) as the output.
The simplest such unit for the addition of binary numbers is called a half-adder. A half-adder may be formed, for example, from four logic elements (Figure 1): two AND gates, an OR gate, and a NOT gate, or inverter. The circuit of a half-adder may vary in accordance with the system of logic elements used.