{"id":3394,"date":"2024-02-08T13:22:41","date_gmt":"2024-02-08T12:22:41","guid":{"rendered":"https:\/\/oopm.org\/?page_id=3394"},"modified":"2024-12-22T20:26:15","modified_gmt":"2024-12-22T19:26:15","slug":"5-3-string-values","status":"publish","type":"page","link":"https:\/\/oopm.org\/?page_id=3394","title":{"rendered":"5.3 String values"},"content":{"rendered":"
\"image_pdf\"<\/a>\"image_print\"<\/a><\/div>\n

In the first version of class Account<\/code>, the owner of the account was represented by a String<\/code> data item. <\/p>\n\n\n\n

class<\/strong> Account(owner: var<\/strong> String):\n   balance: var<\/strong> float\n   interestRate: var<\/strong> float\n   -\"- <\/code><\/pre>\n\n\n\n
The specification var<\/strong> String<\/code> in the declaration of owner<\/code>, specifies that owner<\/code> may hold string values, and String<\/code> is the type of owner<\/code>. <\/p>\n\n\n\n
The type String<\/code> is usually not considered a primitive value type. The reason is that the primitive values may be represented in a fixed number of bytes in the computer, whereas a String<\/code> value may need a variable number of bytes for its representation.<\/p>\n\n\n\n
A string value is a sequence of characters as opposed to char values, which are single characters. A string value may thus consist of zero or more characters. In the program text, a string value is enclosed in double quotes (“) and special characters are preceded by a slash (\\). Example are shown below:<\/p>\n\n\n\n
\"John Smith\"       \n\"Hello world\\n\".          -- a newline is represented by \\n\n\"a + b * (c +111)\"\n\"He said: \\\"Go away!\\\"\"   -- the character \" is represented by \\\"<\/code><\/pre>\n\n\n\n
The method length<\/code> of a String<\/code> returns the number of characters in the String<\/code>, and the method get<\/code> returns the character at a given position in a String<\/code>.<\/p>\n\n\n\n
The following example shows how to get the characters in a given String<\/code> and print them on the console. s: val<\/strong> \"Hello world\" <\/code>specifies that s<\/code> has the value \"Hello world\"<\/code> during the whole program execution.<\/p>\n\n\n\n
s: val<\/strong> \"Hello world\"\nfor (1):to S.length :repeat\n   console.print(S.get[inx])<\/code><\/pre>\n\n\n\n
The default value for a String<\/code> variable is the empty string (\"\"<\/code>).<\/mark><\/p>\n\n\n\n
The get<\/code> method<\/h2>\n\n\n\n
The next example shows how to search for an occurrence of a given character in a String<\/code>. The method assumes that the aName<\/code> holds a name consisting of a first name and a surname, separated by blanks<\/p>\n\n\n\n
aName: val<\/strong> \"John Smith\"\nfirstSurname:\n   i: var<\/strong> integer\n   i := 1\n   while (aName.get[i] <> ' ') :repeat\n       console.print(aName.get[i])\n       i := i + 1<\/code><\/pre>\n\n\n\n
Here we use a while-loop which executes a sequence of statements as long as the condition is True<\/code>. <\/p>\n\n\n\n
The expression aName.get[i] <> ' '<\/code> is the condition that is evaluated before each iteration of the loop. As long as this condition is true, the statements <\/p>\n\n\n\n
console.print(aName.get[i])\ni := i + 1<\/code><\/pre>\n\n\n\n
are executed. The operator <><\/code> means “not equal”, which means that the expression aName.get[i] <> ' '<\/code> is true if aName.get[i]<\/code> is not equal to the character ' '<\/code> (blank).<\/p>\n\n\n\n
As can been seen, i = 1<\/code> in the first iteration and the condition is thus aName.get[1] <> ' '<\/code>, which evaluates to true<\/code> since aName[1] = 'J'<\/code> (the first char in aName<\/code>) which is not equal to the the char ' '<\/code>.<\/p>\n\n\n\n
In the second iteration, i = 2<\/code> and the condition again evaluates to true<\/code> since  aName[2] = 'o'<\/code>.<\/p>\n\n\n\n
Finally when i = 5<\/code>, the condition evaluates to False<\/code>, since aName[5] = ' '<\/code>, and the while-loop terminates.<\/p>\n\n\n\n
String operators<\/h2>\n\n\n\n
A number of operators are available on String<\/code> values.<\/p>\n\n\n\n
The operator '+'<\/code> concatenates two String<\/code> values and return a new String<\/code> value. This is illustrated by the following example:<\/p>\n\n\n\n
S1,S2: var<\/strong> String\nS1 := \"John\" + \" Smith\"\nS2 := \"Hello \" + S1<\/code><\/pre>\n\n\n\n
The expression \"John\" + \" Smith\" <\/code>evaluates to the String<\/code> \"John Smith\"<\/code>, which is then assigned to S1<\/code>. <\/p>\n\n\n\n
The expression \"Hello \" + S1<\/code> evaluates to the String<\/code> \"Hello John Smith\"<\/code>, which is assigned to S2<\/code>.<\/p>\n\n\n\n
The operator '='<\/code> compares two String<\/code> values, and evaluates to true<\/code> if the two Strings<\/code> are identical and false<\/code> if they differ. Consider the following example:<\/p>\n\n\n\n
S1,S2: var<\/strong> String\nS1 := \"John\"\nS2 := \"Liza\"\nS1 = S2  -- false\nS1 <> S2 -- true\nS1 = \"John\" -- true\nS1 = \"john\" -- false<\/code><\/pre>\n\n\n\n
Note that S1 = \"john\"<\/code> evaluates to false<\/code> since the upper-case letter 'J'<\/code> differs from the lower-case letter 'j'<\/code>.<\/p>\n\n\n\n
The operator '<='<\/code> compares two String<\/code> values according to the numerical value of the characters in the strings. <\/p>\n\n\n\n
Immutability<\/h2>\n\n\n\n
A String <\/code>value is immutable, which means that it cannot be changed. There is thus no put<\/code> method on String<\/code> values.<\/p>\n\n\n\n
<\/p>\n
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In the first version of class Account, the owner of the account was represented by a String data item. The specification var String in the declaration of owner, specifies that owner may hold string values, and String is the type of owner. The type String is usually not considered a primitive value type. The reason […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":2270,"menu_order":3,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-3394","page","type-page","status-publish","hentry"],"mb":[],"mfb_rest_fields":["title","gutenberg_elementor_mode"],"_links":{"self":[{"href":"https:\/\/oopm.org\/index.php?rest_route=\/wp\/v2\/pages\/3394","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/oopm.org\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/oopm.org\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/oopm.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/oopm.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=3394"}],"version-history":[{"count":33,"href":"https:\/\/oopm.org\/index.php?rest_route=\/wp\/v2\/pages\/3394\/revisions"}],"predecessor-version":[{"id":10795,"href":"https:\/\/oopm.org\/index.php?rest_route=\/wp\/v2\/pages\/3394\/revisions\/10795"}],"up":[{"embeddable":true,"href":"https:\/\/oopm.org\/index.php?rest_route=\/wp\/v2\/pages\/2270"}],"wp:attachment":[{"href":"https:\/\/oopm.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=3394"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}