HR Kang

Another mistake: 'b>d' --> 'c>b'
Then res==1 will mean sample 1 having more success, and res==-1 the opposite.

It will be useful if output argument feature is added, like following:
function res = McNemarextest(v, t, alpha)
...
if t==1
 if P>alpha
  res = 0;
 else
  if b>d, res=1; else res=-1; end
 end
else
 if P>alpha
  res = 0;
 else
  res = 1;
 end
end

In this way, res will be:
in 2-tailed test, 0 if not significant, 1 if significant
in 1-tailed test, 0 if not significant, 1 if b>d significantly, -1 if b<d significantly.