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The parameter side
is set to 100.
The value 100 is passed
to the Square procedure.

Figure 4-17: Calling the Square procedure with side set to 100
Here, the number 100 (called an argument) is passed to the Square
procedure. When Square is executed, its side parameter is set to 100, and
this value is used to replace all occurrences of the side block inside the pro-
cedure. As you can see, the ability to specify different arguments to a proce-
dure is a powerful feature that adds a lot of flexibility to our programs.
We can enhance our Square procedure even further by making it accept
the square’s color as a second parameter, as shown in Figure 4-18. Here, we
added a second input parameter, called clrNum (short for color number),
which indicates the desired color of the square. The procedure now sets the
pen color to the value specified by clrNum before executing the drawing loop.
Edit the Square block to implement the changes shown in the figure.

Par ameterS VS. argumentS
Although many programmers use the terms parameter and argument inter-
changeably, the two terms are in fact different . To clarify, consider the Average
procedure shown below, which computes the average of two numbers .

num1 and num1
are parameters
to the procedure.
The numbers 100
and 50 are called
arguments.

As defined, this procedure has two parameters named num1 and num2 .
A parameter defines an input to a procedure . You’d call this procedure with the
block shown at the left and specify some values or expressions inside the avail-
able slots . The values 100 and 50 in the above example are called arguments
of the procedure .
Of course, the number of arguments in the procedure call must match the
number of parameters in the procedure’s definition . When you call Average,
the parameters num1 and num2 receive the values 100 and 50, respectively,
because arguments and parameters are matched by position .

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