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:

The exact rules for the allowed values of _leftPosition _and rightPosition are:

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.