programming-for-dummies

Repeating a Subprogram with Recursion 227
This same function as seen in the Python language might look like this:
def convertc2f(temperature):
new = ((9.0/5.0) * temperature) + 32
return new
To run this function, you could use the following program:
temp = 12
print “Temperature in Celsius = “, temp
print “Temperature in Fahrenheit = “, convertc2f(temp)
Repeating a Subprogram with Recursion
In Chapter 5 of this mini-book, you can read about loops that can repeat one
or more commands multiple times. If you want to repeat the commands
stored in a subprogram, you can just call that subprogram from within a
loop, such as
FOR I = 1 TO 4
Subprogram name
NEXT I
Book II
Chapter 6
Breaking a Large
Program into
Subprograms
This example would run all the commands in a subprogram four times.
However, here’s another way to run a subprogram multiple times: recursion.
The idea behind recursion is that instead of defining how many times to run
a subprogram, you let the subprogram call itself multiple times, such as
SUB MySubprogram
MySubprogram
END SUB
When this subprogram runs, it calls itself, essentially making a second copy
of itself, which then makes a third copy of itself, and so on. A common problem
used to demonstrate recursion is calculating a factorial (which multiples
a number by a gradually decreasing series of numbers).
Not every programming language supports recursion, such as some versions
of BASIC.
A factorial is often written like this:
4!
To calculate a factorial, you multiply a number (4, in this case) by a number
that’s one less (3) and keep repeating this until you get the value of 1, such as
4! = 4 * 3 * 2 * 1
= 24