function num = posnum;
num = input('Enter a positive number: ');
n = nargin;
while num<0
fprintf('Error # %.0f : Follow Instructions!\n',n)
...
Reread the documentation for nargin -- it provides only the number of arguments with which a function is called -- and your function has no arguments so it rightfully returns 0--and if you tried to pass an argument, the call to the function would fail for that reason.
You're not interested in how many arguments are being passed to the function at all.
You'll need to keep an internal counter and increment it in the error section of the code.
Also, the above code could never output the last line shown -- the trailing semicolon suppresses output and there's nothing else to output anything -- and it surely appears the answer this case should be 2.
