view signals
add wave -r /*

force a 0         
force b 0         
force cin 0         
run 100ns

force a 1         
force b 0         
force cin 0         
run 100ns

force a 0         
force b 1         
force cin 0         
run 100ns

force a 1         
force b 1         
force cin 0         
run 100ns

force a 0         
force b 0         
force cin 1         
run 100ns

force a 1         
force b 0         
force cin 1         
run 100ns

force a 0         
force b 1         
force cin 1         
run 100ns

force a 1         
force b 1         
force cin 1         
run 100ns