String Expressions

A string expression is an expression whose value is text. It is built from String Constants, Variables, the String Operators, and the many functions that return text.

Writing the Text Itself

A string constant may be written between double quotes or between single quotes. A constant cannot contain the quote character that opened it and cannot run past the end of the line, so the second pair of quotes is what lets a quote character appear inside the text:

print "it's a nice day"
print 'she said "hello"'

displays

it's a nice day
she said "hello"

Joining Text Together

Four operators build longer strings. The full table is on the String Operators page; what matters when reading an expression is that three of them do two different jobs:


Operator	What it does
;	Always joins. Numbers are turned into text first.
+	Joins when either side is a string, adds when both sides are numbers.
&	Joins when either side is a string, ANDs the bits when both sides are numbers.
*	Repeats a string a given number of times.

The decision is made on the type of each value, not on what it looks like. A string of digits is still a string:

print 12 + 3
print "12" + 3
a = "12" ; 3
print a

displays

15
123
123

Repeating works with the string on the left and the count on the right. Written the other way round it is a multiplication, and the text counts as zero:

print "ab" * 3

displays

ababab

A repeat count of zero or less produces an empty string.

Numbers Turned into Text

When a number is joined to a string it is converted exactly as String would convert it, honouring the number of decimal digits set in Options (twelve by default), so a calculated value may not appear with all of the digits it holds.

How Long a String May Be

A string may hold up to 16777216 characters. An operation that would produce a longer one reports an error and the result is cut to that length.

Comparing Text

Comparing two strings with =, <>, <, >, <= or >= produces a true or false answer rather than text; the rules, including what happens when a string is compared against a number, are on the Boolean Expressions page.

Functions That Return Text

Chr, Implode, Left, Lower, Ltrim, Mid, Replace, Right, Rtrim, String, ToBinary, ToHex, ToRadix, Trim and Upper all return a string. Instr, Length and Asc take strings but return a number.

Some string functions accept a Regular Expression instead of plain text to search for.

Availability

Present in BASIC-256 but never described — this page was empty. Written from the BASIC-256 v2.1 continuation project source.