n = input('Enter a positive integer ');
err = 0;
if n ~= abs(round(n)) % What is the purpose of this if-else structure?
    err = 1;
else
    intsum = 0;
    for i=1:n
        intsum = intsum + i;
    end % This ends the for loop
end % This ends the if-else structure
if err
    disp('You must enter a positive integer.')
else
    fprintf('The sum of the integers from 1 to %i is %i\n',n,intsum)
end