how to detect horizontal or vertical lines code on OCTAVE

I created a program that would help a user find the equation of a line while they input values for two points. now i need to figure out how to write the program so it can determine what kind of line will be formed (horizontal or vertical). this is a preview of what my current program lookes like;

x1 = input ('enter value of x1: ')
x2 = input ('enter value of x2: ')
y1 = input ('enter value of y1: ')
y2 = input ('enter value of y2: ')

%find the slope of the line
m = (y2-y1) / (x2-x1);
%find the equation of the line
b = y1-m*x1;
fprintf('Your two points (%d,%d) and (%d,%d) form a line\n', x1,x2,y1,y2);
fprintf('the equation of your line is: y = %.3fx + %.3 f\n',m,b);

[matquest]

The definition of a horizontal line is when the slope (m) = 0. The limit x2 ->x1 of (y2 - y1)/x2-x1 is a vertical line.

Answer 1

[Image Analyst]

if y1 == y2
    % Horizontal line.
elseif x1 == x2
    % Vertical line.
else
    % Slanted line.
end