Page 161 - Concise Encyclopedia of Robotics

IF/THEN/ELSE I
In computers and smart robots, choices must often be made in the execu-
tion of a program. One of the most common programming decision
processes is called IF/THEN/ELSE. It can be expressed as a sentence: “If
A, then B; otherwise (or else) C.”
An example of an IF/THEN/ELSE process is shown in the illustration.
The intent is to determine the absolute value of a real number. Suppose a
computer is working with an input number, designated x. If x is negative
(that is, if x 0), then x must be multiplied by 1 to obtain the absolute
value |x|. If x is zero or positive, then x is equal to its absolute value. The
computer must compare the numerical value of x with zero. The machine
will then output the absolute value of the number, by either multiplying
x by 1 or by leaving x alone.
IF/THEN/ELSE processes are especially useful command structures
for robots. You might tell a robot,“Go to the kitchen and get me a paper
napkin.” The robot controller has a command structure stored on its
hard drive or in memory. It needs an alternative in case there are no
paper napkins in the kitchen. The programming might take the form: “If
this command can be executed, then carry out the task. Otherwise, output
the audio statement, ‘Your order cannot be completed because there are
no paper napkins in the kitchen.’”

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