The only problem you would run into is if the norm of V is zero (or very close to it). This could give you Inf or NaN when you divide, along with a divide-by-zero warning. If you don't care about getting an Inf or NaN, you can just turn the warning on and off using WARNING:
oldState = warning('off','MATLAB:divideByZero'); % Return previous state then
% turn off DBZ warning
uV = V/norm(V);
warning(oldState); % Restore previous state
If you don't want any Inf or NaN values, you have to check the size of the norm first:
normV = norm(V);
if normV > 0, % Or some other threshold, like EPS
uV = V/normV;
else,
uV = V; % Do nothing since it's basically 0
end
If I need it in a program, I usually put the above code in my own function, usually called unit (since it basically turns a vector into a unit vector pointing in the same direction).