Substring

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In BR, a substring of a string is a subset of the symbols in a string, where the order of the elements is preserved.

Therefore, "ball" is a substring of "snowball", but "bow" is not. Even though all the letters in "bow" are also contained in "snowball", they are not in the same order.

In order to extract a substring from its parent string, we must use a start and stop subscripts. The syntax

parent$(start:stop)

denotes "the substring of string parent$ starting at character start and ending at character end"

Below is an example of how subscripts can be used to extract substrings from strings:

00010 dim a$*255, b$*255
00020 let a$ = "from this long string, choose these words"
00030 let b$ = a$(24:41)
00040 print b$

The output of the above example will be:

choose these words

Modify

A BR String may be modified using its subscripts. For example, A$(4:6) uses the substring of A$ beginning with position 4 up to and including position 6; the numbers inside the parentheses could be replaced by any numeric expression. In the following example, line 40 sets element 3 of array Z$ to "XXC":

00010 LET Z$(3) = "ABC"
00020 LET A = 1
00030 LET B = 2
00040 LET Z$(3)(A:B) = "XX"

In the next example, line 40 replaces "BC" with "23" and assigns the value "A23D" to X$:

00030 LET X$ = "ABCD"
00040 LET X$(2:3) = "23"

Note that you the number of characters being replaced does not have to match the number of characters they are being replaced with. Consider the following example:

00010 dim a$*255
00020 let a$ = "beginning end"
00030 let a$(10:10) = " middle " ! here we are replacing one character (a space) with 6 characters (" middle ")
00040 print a$

The result of the example above is

beginning middle end


Insert


Prepend

To prepend string1$ to string2$ means to join string1$ to the beginning of string2$.

To append to the beginning of a string you should use

X$(0:0)="append this to front"

or alternately

X$(1:0)="append this to front"

For example,

00010 dim result$*255 ! dimension long enough to fit the result
00020 let result$ = " and this is the end"
00030 let string_to_prepend$ = "this is the front"
00040 let result$(0:0) = string_to_prepend$
00050 print result$

The output of the program above will be:

this is the front and this is the end


Append

To append string2$ to string1$ means to join string2$ to the end of string1$.

To append to the end of a String you should (for maximum speed of code execution) use

X$(inf:0)="append this to end"

OR

X$(inf:inf)="append this to the end"

Here, inf denotes infinity.

So X$(inf:inf) means "the substring of X$ starting at infinity". This is particularly useful when you don't know how long your string is and do not want to calculate its length.

see also: prepend


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