Why am I getting the error : Operands to the || and && operators must be convertible to logical scalar values for the below code?

function yq = myInterp(X, Y, xq)

step = 1; stop = length(X);

for i = 1:step:stop;

    %If xq is a value in the road generator, then use that number
    if xq == X(i)
        yq = Y(i);
        break

    %If xq is in between two numbers in the road generator, the use interpolation 

    elseif (xq > X(i) && xq < X(i+1))

        yq = Y(i)+(Y(i+1)-Y(i))*(xq-X(i))/(X(i+1)-X(i));
        break

end

end

Answer 1

[Andrei Bobrov]

X = [0 2 5 20 40]';
xq = 40*rand(20,1);
xq(3)= 1.3;
xq(5) = 5;
Y = [2 5 8 40 60]';

function  yq = myInterp(X, Y, xq) % without loop
    dyx = diff(Y)./diff(X);
    [~,c] = histc(xq,X);
    yq = Y(c) + dyx(c).*(xq - X(c));
end

function yq = myInterp(X, Y, xq) % with loop
    n = length(X);
    yq = zeros(size(xq));
    for ii = 1:n-1
        t = xq >= X(ii) & xq < X(ii+1); % '&' for array, '&&' for scalar
        yq(t) = Y(ii)+(Y(ii+1)-Y(ii))*(xq(t)-X(ii))/(X(ii+1)-X(ii));
    end
end