% MT 03 2018/19
% Problem Set 2, Exercise 2

E_in = input('Enter the value of the energy converted: ');
E_in_units = input('Enter the current units (J, cal, eV): ', 's');
E_out_units = input('Enter the new units (J, cal, eV): ', 's');

error = 0;

switch E_in_units
    case 'J'
        EJ = E_in;
    case 'cal'
        EJ = E_in / 0.239;
    case 'eV'
        EJ = E_in / 6.24e18;
    otherwise
        error = 1;        
end

switch E_out_units
    case 'J'
        E_out = EJ;
    case 'cal'
        E_out = EJ * 0.239;
    case 'eV'
        E_out = EJ * 6.24e18;
    otherwise
        error = 1;        
end
        
if error
    disp('Error! Current or new units typed incorrectly');
else
    fprintf('E = %g %s \n', E_out, E_out_units);
end