7.2: 'if' and 'switch' commands

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We discuss the constructs if\elseif\else and switch\case\otherwise in this section.

Suppose we want to have part of our program run only under certain conditions. For this, we use an if\else structure. The basic format of this structure is:

if (put condition(s) here)(put calculations here to be run if the conditions are met)
elseif (other condition(s))(calculations that will run under the new conditions)(more elseif statements, if desired)
else (calculations run if none of the previous conditions are met)
end

Example 7.3.1: Using if

Let’s write a script M-file that lets a user input a number and then displays if that number is less than 5, between 5 and 10 (inclusive), or greater than 10.

number = input('Input a number ');
if number < 5
disp('Your number is less than 5.')
elseif number >=5 && number <= 10
disp('Your number is between 5 and 10.')
else
disp('Your number is greater than 10.')
end

Try running this program using various numbers for input.

The switch\case structure is similar to the if structure, but has a few advantages. First of all it is easier to read and second, it is better if you are comparing strings (of possibly different lengths). The basic format is:

switch (expression to test)
case (case condition)
(output in that case)
case (case condition)
(output in that case)

...(more cases)
otherwise
(do this if no cases are met)

end

Example 7.3.2: Using switch

Let’s check to see if a cadet is in his\her first two years at VMI.

Year = 'second class';

switch Year
case {'fourth class','third class'}
disp('You are in the first two years.')
case {'second class','first class'}
disp('You are in the last two years.')
otherwise
disp('You must be a 5th year.')

end

The cases are grouped by curly brackets so that a case will be satisfied if the value of Year is any of the values in a specific case. Once this code is executed, the switch command will look at the value of Year and the output should be

You are in the last two years.