substring

#substring

##Syntax A substring is one of:

(a) stringReference ( leftPosition .. rightPosition ) (b) stringReference ( charPosition )

##Description A substring selects a part of another string. In form (a) the substring starts at the left position and runs to the right position. In form (b), the substring is only a single character. Turing support substrings of char(n) values.

##Example

    var word : string := "bring"
    put word (2 .. 4)       % Outputs rin
    put word (3)        % Outputs i
    put word (2 .. *)       % Outputs ring; the star (*) means
                    % the end of the string.
    put word (* - 2 .. * - 1 )  % Outputs in

##Details The leftmost possible position in a string is numbered 1. The last position in a string can be written as an asterisk (*). For example, word (2 .. *) is equivalent to word (2 .. length(word)).

Each of leftPosition, rightPosition, and charPosition must have one of these forms:

(a) expn (b) * (c) * - expn

The exact rules for the allowed values of leftPosition and rightPosition are:

(1) leftPosition must be at least 1, (2) rightPosition must be at most length (stringReference), and (3) the length of the selected substring must zero or more.

This specifically allows null substrings such as word (1, 0) in which rightPosition is 0 and word (6, 5) in which leftPosition is one more that length (stringReference).

Note that substrings are not assignable. For example, if s is a string, the statement s (3) := "a" is illegal in Turing.

Turing supports substrings of char(n) values. See char(n). If a substring of char(n) value t has two operands, as in t(2..77), the result type of this operation is a string. If the substring has one operand, as in t(7), this becomes, in effect, a subscript into an array of characters. The result is a reference to a char, which can be assigned to or passed to a var parameter.

##See also string1.html, char.html, char.html(n), explicitstringconstant.html, explicitcharconstant.html, catenation and length.html.