5.5: The if-else Statement

An if-else statement is used when there are two possible actions. If the condition is true, MATLAB runs the first action. Otherwise, MATLAB runs the second action.

if condition
action1
else
action2
end

In the following example, the user is asked to enter the diameter of a circle. If the diameter is invalid, the program prints an error message. Otherwise, it calculates the perimeter.

% circlePerimeter.m
% This script calculates the perimeter of a circle.
% It also checks whether the diameter is valid.

diam = input('Please enter the diameter: ');

if diam <= 0
    fprintf('Sorry; %.2f is not a valid diameter.\n', diam)
else
    perimeter = pi * diam;
    fprintf('For a circle with diameter %.2f, ', diam)
    fprintf('the perimeter is %.2f.\n', perimeter)
end

If the user enters -1, for example, the message will be: Sorry; -1.00 is not a valid diameter.
If the user enters 2, for example, the message will be: For a circle with diameter 2.00, the perimeter is 6.28.