String Type

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The string data type is a structured type.

It is intended for the representation and manipulation of character strings.

A character string is an ordered sequence of characters.

A string variable contains a character string.

Syntax: declaring a string variable

var
   identifier : string [size];

• size is an integer constant determining the maximum number of characters that the variable can contain.
• If size is not specified, then the maximum size is limited to 255.

Example

var
   s : string [80];
begin
   s := 'algorithm';
   writeln(s);
end.

• The declaration of the variable s creates an array[0..80] of char.
• The first character of the string is s[1], the second is s[2], etc.
• The current length of the string is encoded in s[0], its value is
  ord(s[0]).
• Since the current length is encoded on a char, it is limited to 255.

Concatenation and length

Concatenating two strings consists of juxtaposing them.

Example

program example;
var
   s, s1, s2 : string [80];
   len : integer;
begin
   s1 := 'algorithm';
   s2 := 'program';
   s := s1 + ' and ' + s2;     { concatenation }
   writeln(s);
   len := length(s);     { length of s }
   writeln(len);
end.

• The + operator is the concatenation operator.
• The length() function returns as a result the current length of a string data type.

Comparison operators

In a Boolean expression, comparison operators are used to compare two string data type values.

The comparison is performed character by character according to the lexicographic order of the ASCII code.

Example
The Boolean expression ('AB' < 'B') evaluates to true.

Program: palindrome

A palindrome is a word whose letter order remains the same whether read from left to right or from right to left.
Examples of palidromes: kayak, noon, level, civic.

The following program checks if a word is a palindrome.

program example;
var
    str, backward : string;
    k : integer;
begin
    str := 'level';
    str := lowercase(str);
    backward := '';
    for k := length(str) downto 1 do
        backward := backward + str[k];
    if str = backward then
        writeln(str, ' : is a palindrome')
    else
        writeln(str, ' : is not a palindrome')
end.