Part 2

Introducing Prt_Btwn() - the Substring function

Prt_Btwn () (pronounced as "part between") retrieves a substring located between the specified positions of the original string:

Prt_btwn (firstPsn, lastPsn, whichString);

Let's look at the example. We have a string of five integers. We will write position numbers between the integers starting with position zero (before the first item in the string), and ending with position following the last item in the string, as shown below.

α =		<7,		9,		4,		1,		3>;
	0		1		2		3		4		5

Integer 7 is located between positions 0 and 1, 9 is between positions 1 and 2, etc.

Now we want to extract a substring using the operation shown below:

Prt_btwn (1, 4, α );

The substring between positions 1 and 4 is <9, 4, 1 >:

α =		<7,		9,		4,		1,		3>;
	0		1		2		3		4		5

If we want our substring to include the first element of the original string, we will use 0 as the starting position:

Prt_btwn (0, 4, α ) = <7, 9, 4, 1 >;