Potential Difference Among 3 Resistors

%% Potential Difference Across 3 Resistors
% Determines the voltage from point A to B when two resistors are in
% parallel and the other is in series. Notes and clarifications are
% at the bottom of the code.

clc, clear

resis = input('Input the resistances in brackets\n');
a = input('Are you given the current across the resistors in series or parallel?\n');

switch a
    case 1
        I(1) = input('What is the current across R1?\n');
        V(1) = I(1) * resis(1);
        V(2) = (I(1)*resis(2)*resis(3))/(resis(2)+ resis(3));
        Vsum = sum(V);
    case 2
        b = input('Are you given the current is across R2 or R3?\n');
        switch b
            case 1
                I(2) = input('What is the current across R2?\n');
                V(2) = I(2) * resis(2);
                I(3) = V(2)/resis(3);
                V(1) = (I(2) + I(3))*resis(1);
                Vsum = sum(V);
            case 2
                I(3) = input('What is the current across R3?\n');
                V(3) = I(3) * resis(3);
                I(2) = V(3)/resis(2);
                V(1) = (I(2) + I(3))*resis(1);
                Vsum = sum(V);
        end % switch b
end
fprintf('The potential difference across the resistors is %.3e V', Vsum);

%{
It is important for this code that the array 'V' be empty at the start
    because later on sum(V) is used and only the values calculated
    should be calculated.
Potential difference is the same as the voltage.
This code works under the assumption that R2 and R3 are in parallel with one
    another and that R1 would be in series.
When prompted, the user needs to put the resistors in brackets [] for the
    code to work.
The output is rounded to three places after the decimal point. This can be
    changed or removed by adjusting the .# in the fprintf line.
%}