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8/3/2019 Tern Paper of Data

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Term Paper of Data StructureOn

Operations on Strings

DOS:12/19/2008

Submitted By:

Name: Shruti ThakurRoll no.: 10Reg.:3010070235

Course: BCA-MCA Dual IntegratedSection: A


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Operations on Strings 200

8

AcknowledgementI would like to express my gratitude to all those who gave me helping hand in completing this

term paper. I want to thank my teacher Miss. Rajdeep Kaur for helping me whenever I needed it

the most. My friends have also supported me in my work. I want to thank them all for their help,

support, interest and valuable hints.

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Contents

Topics Page no.

Introduction 4-5

Operations on Strings 6-26

Conclusion 27

References 28

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Introduction

String is a sequence of characters enclosed in quotes. E.g. Hello

String processing is one of the most important and most frequent applicationsof a computer

Java recognizes this fact and therefore provides special support for strings to

make their use convenient

Every string is an instance of Javas built in String class, thus, Strings are

objects.

Declaration

Like any object, a string can be created using new as in the following example:o String str1 = new String(Hello dear);

However, as an extra support, Java allows String object to be created without

the use of new, as in:

o String str2=How are you;

This is inconsistent with the way Java treats other classes.

String objects are represented as a sequence of characters indexed from 0.

Example: String greeting = Hello, World;

H e l l o . W o R l d !

0 1 2 3 4 5 6 7 8 9 10 11 12

A common operation on Strings is extracting a substring from a a given string.

Java provides two methods for this operation:

Another special feature of Strings is that they are immutable. That is, once a string

object is created, its content cannot be changed. For example, consider the following: String str1 = Hello World;

str1 = str1.substring(4);

Instead of changing the str1 object, another object is created. The former is garbage

collected, thus, the reference to the former is lost.

The fact that Strings are immutable allows the Java system to process Strings very

efficiently.

For example, consider the following:

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String str1 = Hello;

String str2 = Hello;

We would expect the following

But in fact, this is what happens

The Java system is smart enough to know that the two strings are identical and allocatessame memory location for the two objects

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Operations in String

ABBREV

Tests if one string is an abbreviation of another string. An abbreviation is a substring

that starts at the beginning of a string. For example, 'auto' could be an abbreviation for

'automobile'.

Syntax:

result = ABBREV(string, abbreviation, length)

stringis the string (for which abbreviation may be an abbreviation).

abbreviation is a possible abbreviation ofstring.

length is the minimum length that abbreviation must be in order to beconsidered as an abbreviation. Iflength is omitted, there is no restriction upon

abbreviation's minimum length (and therefore an empty string would beconsidered an abbreviation for any other string).

Returns

1 ifabbreviation is an abbreviation ofstring, or 0 if not.

Notes

ABBREV() is case sensitive, and leading/trailing spaces are not stripped off before

the two strings are compared.

Examples

Example Use Output

ABBREV('Foobar', 'Foo') 1

ABBREV('Foobar', 'Foo', 4) 0 /* 'Foo' isn't at least 4 chars */

ABBREV('Foobar', 'foo') 0 /* Different case - 'F' versus 'f' */

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CENTER

Returns a string formatted to fit centered within a certain number of characters. Ifnecessary, the string's size is decreased to fit into that many characters, or pad

characters are used to fill out the new string with the original string centered within

the new string.

Syntax:

formatted = CENTER(string,length,padchar)

stringis the original string (to format).

length is the desired length of the final string. If length is less than the size ofthe original string, then characters will be deleted from the front and end of the

string in order to fit the desired length. If length is greater than the size of the

original string, then the original string will be centered within the new string

andpadcharcharacters will be used to fill out the new string to the desiredlength. length must not be negative, nor have a fractional component -- it must

be a positive whole number.

padchar is the character to use for padding (if the original string is notalready >= the desired length). Ifpadcharis omitted, the default is a space

character.

Returns

A copy of the original string extended to the desired length, with the original string

centered within the new string, and padchars filling out the new string.

Notes

The original string is not altered. Only the returned value from CENTER is formatted.

If length is an odd number, any extrapadcharis placed on the right-hand side of thecentered, original string.

Examples

Example Use Result

CENTER('Foobar',10) ' Foobar '

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CENTER('Foobar',11) ' Foobar '

CENTER('Foobar',3) 'oob'

CENTER('Foobar',4) 'ooba'

CENTER('Foobar',10,*) '**Foobar**'

CHANGESTR

Exchanges any occurence of one substring (within a given string) with another

substring.

Syntax:

newstring = CHANGESTR(searchfor, string, exchange)

string is the original string (to exchange substrings within).

searchfor is which substring to search for (withinstring. Ifsearchforis anempty string, then no exchange is performed, and the original string is returned.

exchange is the substring to insert in place ofsearchfor, whereversearchforoccurs withinstring. Ifexchange is an empty string, then each occurence of

searchforis deleted without being replaced by anything.

Returns

A copy of the original string with all occurences ofsearchforreplaced with exchange.

Notes

The original string is not altered.

Examples

Example Used Output

CHANGESTR('a', 'fred', 'c') 'fred'

CHANGESTR('', '', 'new string') ''

CHANGESTR('a', 'abcdef', 'x') 'xbcdef'

CHANGESTR('0', '0', '1') '1'

CHANGESTR('a', 'def', 'xyz') 'def'

CHANGESTR('a', '', 'x') ''

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CHANGESTR('a', '', 'x') 'def'

CHANGESTR('abc', 'abcdef', 'xyz') 'xyzdef'

CHANGESTR('abcdefg', 'abcdef', 'xyz') 'abcdef'

COMPARE

Compares two strings for inequality, and returns the position where they differ.

Syntax:

result = COMPARE(string1, string2, padchar)

string1 and string2 is the two strings to be compared. If one of the strings is shorter than the other,padcharis the character used to

pad out the shorter string to the same length as the longer string. Ifpadcharisomitted, then by default, the shorter string is padded with extra spaces.

Returns

0 if both strings are equal. If not equal, then the first position where the two strings are

different is returned (where 1 is the first character in the strings).

Notes

COMPARE() is case-sensitive, so 'BLORT' does not equal 'blort'. Use

TRANSLATE() or the UPPER keyword to upper-case the strings prior to

COMPARE(), if desired.

Leading and trailing spaces do matter, so ' blort ' does not equal 'blort'. Use STRIP() to

removed leading/trailing space prior to COMPARE(), if desired.

Example

Examples Used OutputCOMPARE('FooBar', 'Foobar') 4COMPARE('Foobar', 'Foobar') 0COMPARE('Foobarrr', 'Fooba') 6COMPARE('Foobarrr', 'Fooba', 'r') 0

COPIES

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http://www.ulisoft.org/rexx_referenz/funcs2.htm#TRANSLATEhttp://www.ulisoft.org/rexx_referenz/funcs2.htm#STRIPhttp://www.ulisoft.org/rexx_referenz/funcs2.htm#TRANSLATEhttp://www.ulisoft.org/rexx_referenz/funcs2.htm#STRIP


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Creates a new string that is another string concatenated (ie,

appended) a specified number of times.

Syntax:

newstring = COPIES(string, total)

string is the original string (to append). Ifstringis an empty string, then theresulting newstring is also an empty string.

total is a count of how many times to appendstring. totalcannot be negative,nor have a fractional component -- it must be a positive whole number. Iftotalis 0, an empty string is created.

Returns

The new string comprised oftotalinstances ofstringappended.

Examples:

Example Used Output

COPIES('Foo', 3) 'FooFooFoo'

COPIES('*', 16) '****************'

COPIES('Bar ', 2) 'Bar Bar '

COPIES('', 10000) ''

COUNTSTR

Counts how many occurences of a substring are within another string.

Syntax:

howmany = COUNTSTR(searchfor, string)

string is the original string (to search forsearchforwithin).

searchfor is which substring to search for withinstring. Ifsearchforis anempty string, then 0 is returned to indicate no occurrences ofsearchforwithin

string.

Returns

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A count of how many occurrences ofsearchforappear withinstring.

Example

Example Used OutputCOUNTSTR('', '') 0COUNTSTR('a', 'abcdef') 1COUNTSTR(0, 0) 1COUNTSTR('a', 'def') 0COUNTSTR('a', '') 0COUNTSTR('', 'def') 0COUNTSTR('abc', 'abcdef') 1COUNTSTR('abc', 'abcdef') 0COUNTSTR('abc', 'abcdefabccdabcd') 3

COUNTSTR('aaa', 'aaaaaa') 2

DELSTR

Removes one or more characters from a string.

Syntax:

newstring = DELSTR(string, start, length)

string is the string to remove characters from.

start is which character number to start removing from, where 1 would be tostart removing at the first character in the string. If there are less characters in

the string thanstart, then no characters are removed.

length is the desired number of characters to remove (withinstring), startingat (ie, including) thestartcharacter. Iflength is omitted, then the default is to

remove all character from thestartcharacter to the end of the string. lengthcannot be negative, nor have a fractional component -- it must be a positive

whole number.

Returns

A copy of the original string without the removed characters.

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Notes

It is not an error ifstartorlength (or a combination of them) refers to more charactersthan string actually contains.

The original string is not altered. Only the returned value from DELSTR has

characters removed.

Example:

Example Used Output

DELSTR('Foobar', 3) 'Foo'

DELSTR('Foobar', 3, 2) 'Foor'

DELSTR('Foobar', 3, 4) 'Foo'

DELSTR('Foobar', 7) 'Foobar'

EXPAND

Replaces tab characters with spaces, or vice versa.

Syntax:

newstring = EXPAND(string, options, tablewidth2, tablewidth2, )

string is the string to replace characters within.

options is the desired operation. It is one of the following:

>Optio

n Meaning

'S' Replace each tab character with an appropriate number of spaces

based upon the tabwidth args.

'T' Replace space characters with a tab character based upon the

tabwidth args.

If omitted, options defaults to 'S'.

tabwidth1 is the desired width of the first tab stop. For example, a value of'8' would put the first tab stop at the eighth character. If omitted, tabwidth1

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defaults to 8. There may be more tabwidth arguments supplied. For example, if

tabwidth2 is supplied, then this sets the width of the second tab stop. For

example, a value of '8' would effectively put the second tab stop at the sixteenth

character. If there are more spaces/tabs to be replaced than there are tabwidths

specified, then the value of the last tabwidth is used for all subsequentreplacements.

Returns

A copy of the original string with the space/tab characters replaced.

Notes

The first character instringis presumed to be at a tabstop.

The original string is not altered. Only the returned value from EXPAND has

characters replaced.

Some interpreters do not support this function.

Example:

Example Used Output

EXPAND(' Foo bar', 'T', 3) '09'X || 'Foo' || '09'X || 'bar'

EXPAND(' Foo bar', 'T') ' Foo bar'

EXPAND(' Foo bar', 'T', 3) ' Foo' || '09'X || ' bar'

EXPAND(' Foo bar', 'T') '09'X || 'Foo bar'

EXPAND(' Foo bar ', 'T', 3, 3, 6) '0909'X || ' Foo' || '09'X || ' bar '

INSERT

Inserts a substring into another string.

Syntax:

Newstring = INSERT(insert, string, position, length, padchar)

insert is the substring to be inserted (intostring).

string is the string into which insertis inserted.

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position is the desired character position (withinstring) after which to insertinsert. A position of 0 would cause insertto be inserted before the firstcharacter instring(ie, at the very start). A position of 1 would cause insertto

be inserted after the first character instring(ie, at the very start). Ifposition is

greater than the number of characters instring, then insertwill be inserted afterthe last character ofstring. Ifposition is omitted, then it defaults to 0.

length is the desired length forinsert. Ifinsertis larger, then characters willbe deleted from the end of the string in order to fit the desired length. Ifinsert

is smaller, then it is padded out withpadcharcharacters at the end to fit thedesired length. length must not be negative, nor have a fractional component --

it must be a positive whole number. Iflength is omitted, then no truncation norpadding is performed upon insert.

padchar is the character to use for padding (if the insertis not already >=

length). Ifpadcharis omitted, the default is a space character.

Returns

A copy of the original string with insertinserted into it.

Notes

The original string is not altered. Only the returned value from INSERT has the

inserted substring.

Example:

Example Used Output

INSERT('first', 'SECOND') 'SECONDfirst'

INSERT('first', 'SECOND', 3) 'fiSECONDrst'

INSERT('first', 'SECOND', 3, 10) 'fiSECOND rst'

INSERT('first', 'SECOND', 3, 10, *) 'fiSECOND****rst'

INSERT('first', 'SECOND', 3, 4) 'fiSECOrst'

INSERT('first', 'SECOND', 8) 'first SECOND'

LASTPOS

Finds the last occurrence of a substring within another string.

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Syntax:

Where = LASTPOS(searchfor, string, start)

searchfor is which substring to search for (withinstring. Ifsearchforis anempty string, then 0 is returned to indicate no occurrences ofsearchforwithin

string.


start is which character position to start the backward search from, where 1would be to start searching backwards at the first character instring. If omitted,

the default is to start searching from the last character.startmust not benegative, nor have a fractional component -- it must be a positive whole

number.

Returns

Ifsearchforis found, then LASTPOS() returns the character position where the lastoccurrence ofsearchforoccurs withinstring(where 1 is the first character within

string). Ifsearchforis not found, then LASTPOS() returns 0.

Examples

Example Used Output

LASTPOS('be', 'to be or not to be') 17LASTPOS('be', 'to be or not to be', 10) 3LASTPOS('is', 'to be or not to be') 0

LEFT

Excerpts one or more characters from the left-hand side of a string.

Syntax:

excerpt = LEFT(string, length, padchar)

string is the original string (from which to excerpt characters).

length is the number of characters to be excerpted. Iflength is 0, nocharacters are excerpted. Iflength is greater than the number of characters in

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string, then the excerpt is padded out withpadcharcharacters to the desiredlength.

padchar is the character to use for padding (if the original string is not >=length). Ifpadcharis omitted, the default is a space character.

Returns

A string containing the excerpted characters.

Notes


Example:

Example Used Output

LEFT('Foo bar', 5) 'Foo b'

LEFT('Foo bar', 3) 'Foo'

LEFT('Foo bar', 10) 'Foo bar '

LEFT('Foo bar', 10, '*') 'Foo bar***'

LENGTH

Counts the number of characters in a string.

Syntax:

howmany = LENGTH(string)

string is the string (whose length is to be calculated).

Returns

A count of how many characters are in the string.

Notes

Leading and trailing spaces are counted. You may wish to use STRIP first to trim

those spaces.

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Example:

Example Used Output

LENGTH('') 0

LENGTH('Foo') 3LENGTH(' Foo bar ') 7LENGTH(' foo bar ') 10

OVERLAY

Overlays a substring into another string. OVERLAY() differs from INSERT() in that

OVERLAY() overwrites characters in the string.

Syntax:

newstring = OVERLAY(overlay, string, position, length, padchar)

overlay is the substring to be inserted (intostring).

string is the string into which overlay is overlaid.

position is the desired character position (withinstring) at which to overlay overlay.A position of 1 would cause overlay to be overlaid at the first character instring(ie, atthe very start). Ifposition is greater than the number of characters instring, then the

new string will be padded out withpadcharcharacters and then overlay will beinserted after those pad characters. Ifposition is omitted, then it defaults to 1.

length is the desired length foroverlay. Ifoverlay is larger, then characters will bedeleted from the end in order to fit the desired length. Ifoverlay is smaller, then it is

padded out withpadcharcharacters at the end to fit the desired length. length must

not be negative, nor have a fractional component -- it must be a positive whole

number. Iflength is omitted, then no truncation nor padding is performed upon

overlay.

padchar is the character to use for padding (if the overlay is not already >= length).Ifpadcharis omitted, the default is a space character.

Returns

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A copy of the original string with overlay overlaid in it.

Notes

The original string is not altered. Only the returned value from OVERLAY has theoverlaid substring.

Example Used Output

OVERLAY('NEW', 'old-value') 'NEW-value'

OVERLAY('NEW', 'old-value', 4) 'oldNEWlue'

OVERLAY('NEW', 'old-value', 4, 5) 'oldNEW e'

OVERLAY('NEW', 'old-value', 4, 5, *) 'oldNEW**e'

OVERLAY('NEW', 'old-value', 4, 2) 'oldNEalue'

OVERLAY('NEW', 'old-value', 8) 'old-valuNEW'

OVERLAY('NEW', 'old-value', 11) 'old-value NEW'

OVERLAY('NEW', 'old-value', 4, 2) 'oldNEalue'OVERLAY('NEW', 'old-value', 9) 'old-valuNEW'

POS

Finds the first occurrence of a substring within another string.

Syntax:

where = POS(searchfor, string, start)

searchfor is which substring to search for (withinstring. Ifsearchforis anempty string, then 0 is returned to indicate no occurrences ofsearchforwithinstring.


start is which character position to start the search from, where 1 would be tostart searching at the first character instring. If omitted, the default is to startsearching from the first character.startmust not be negative, nor have a

fractional component -- it must be a positive whole number.

Returns

Ifsearchforis found, then POS() returns the character position where the firstoccurrence ofsearchforoccurs withinstring(where 1 is the first character within

string). Ifsearchforis not found, then POS() returns 0.

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Example:

Example Used Output

POS('be', 'to be or not to be') 4

POS('to', 'to be or not to be',10) 17POS('to', 'to be or not to be',18) 0POS('is', 'to be or not to be') 0

REVERSE

Reverses the order of characters in a string.

Syntax:

newstring = REVERSE(string)

string whose characters are to be reversed.

Returns

A copy of the original string with the order of its characters reversed.

Notes

The original string is not altered. Only the return value of REVERSE has its

characters reversed.

Example:

Example Used Output

REVERSE('FooBar') 'raBooF'

REVERSE(' Foo Bar') 'raB ooF '

REVERSE('3.14159') '95141.3'

RIGHT

Excerpts one or more characters from the right-hand side of a string.

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Syntax:

excerpt = RIGHT(string, length, padchar)

string is the original string (from which to excerpt characters). length is the number of characters to be excerpted. Iflength is 0, no characters

are excerpted. Iflength is greater than the number of characters instring, thenthe excerpt is padded out on the left withpadcharcharacters to the desired

length.

padchar is the character to use for padding (if the original string is not >=length). Ifpadcharis omitted, the default is a space character.

Returns


Notes


Examples

Example Use Output

RIGHT('Foo bar', 5) 'o bar'

RIGHT('Foo bar', 4) ' bar'RIGHT('Foo bar', 10) ' Foo bar'

STRIP

Removes leading and/or trailing space (or other) characters from a string.

Syntax:

newstring = STRIP(string, option, padchar)

string whose leading and trailing space characters are to be removed.

padchar is the character to strip. Ifpadcharis omitted, the default is a spacecharacter.

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option determines whetherpadchars are stripped from the beginning and/orend ofstring. It must be one of the following:

Optio

n Meaning

L (Leading) Only leading characters are stripped. Trailing

characters are not.

T (Trailing) Only trailing characters are stripped. Leading

characters are not.

B (Both) Both leading and trailing characters are stripped.

If omitted, option defaults to 'B'.

Returns

A copy of the original string with its leading and trailing space characters removed.

Notes

The original string is not altered. Only the return value of STRIP has its

leading/trailingpadchars removed.

This removes only thosepadchars appearing at the front or end of the string. Todeletepadchars within the string, use SPACE().

Whenpadcharis omitted, Reginald strips TAB characters as well as space characters.

Other interpreters may strip only space characters (ie, not TAB).

Example

Example Used Output

STRIP(' FooBar') 'FooBar'

STRIP(' Foo Bar ') 'Foo Bar'STRIP(' Foo Bar ', 'L') 'Foo Bar '

STRIP(' 3.14159 ') '3.14159'

STRIP('*** Foo *** Bar ***', ,'*') ' Foo *** Bar'

SUBSTR

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Excerpts one or more characters from a string, and returns that excerpt.

Syntax:

excerpt = SUBSTR(string, start, length, padchar)

string is the original string (from which to excerpt characters).

start is which character position to start the excerpt from, where 1 would be tostart the excerpt at the first character in the string. If there are less characters in

the string thanstart, then an empty string is returned.startcannot be 0 ornegative, nor have a fractional component -- it must be a positive whole

number.

length is the number of characters to be excerpted, starting at the characterpositionstart. Iflength is omitted, the default is to excerpt all characters from

startto the end of the string. Iflength is 0, no characters are excerpted. lengthcannot be negative, nor have a fractional component -- it must be a positive

integer.

padchar is the character to use for padding (if the original string is not >=length +start). Ifpadcharis omitted, the default is a space character.

Returns


Notes

Any leading or trailing spaces are not trimmed from the excerpt.

It is not an error ifstartorlength (or a combination of them) refers to more characters

than string actually contains.


Example

Example Used Output

SUBSTR('Foo bar', 3) 'o bar'

SUBSTR('Foo bar', 3, 3) 'o b'

SUBSTR('Foo bar', 4, 6) ' bar '

SUBSTR('Foo bar', 4, 6, '*') ' bar**'

SUBSTR('Foo bar', 9, 4, '*') '****'

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TRANSLATE

Translates characters in a string to other characters, or makes a string uppercase.

Syntax:

newstring = TRANSLATE(string, tableout, tablein, padchar)

string is the original string (to translate).

tablein is a string containing upto 256 characters, representing characters that

you wish translated to the respective characters in tableout. If one or both of the tables are specified, each character instringthat exists in

tablein is translated to the character in tableoutthat occupies the same position asthe tablein character. Characters instringwhich are not found in tablein are left

unchanged.

If omitted, tablein defaults to all 256 characters of the computer's default

character set. If omitted, tableoutdefaults to an empty set.Iftableoutis largerthan tablein, the extra entries are ignored.

If smaller than tablein, tableoutis padded withpadcharcharacters to the samelength as tablein. Ifpadcharis omitted, the default padding is space characters.

If both of the tables are omitted, TRANSLATE() upper-casesstring.

If a character occurs more than once in tablein, only the first occurrence will

matter.

Returns

A copy of the original string with each tablein character translated to its respective

tableout's character.

Notes

The original string is not altered. Only the return value of TRANSLATE has its

characters translated.

Some REXX interpreters support the UPPER keyword which can be used to translate

the value of a variable.

/* Upper-case My_Variable's value. */

UPPER My_Variable

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You can also specify a variable whose value is the name of the

variables whose values you wish upper-cased. You put that

variable's name in parentheses.

/* Upper-case My_Variable's and Something.1's values. */these = 'My_Variable Something.1'

UPPER (these)

Examples

Examples Used Output

TRANSLATE('FooBar') 'FOOBAR'

TRANSLATE('FooBar', 'ABFORabfor',

'abforABFOR')

'fOObAR'

TRANSLATE('FooBar', 'abfor') 'F B 'TRANSLATE('FooBar', 'abfor', , '#') 'F##B##'

VERIFY

Tests if any characters of one string also occur in another string.

Syntax:

Where = VERFY(string, Lookfor, option, start)

string is the string to search (forlookfor).

start is which character number to start searching from, where 1 would be tostart searching at the first character in the string. If there are less characters in

the string thanstart, then a 0 is returned to indicate that no characters in lookformatched.

option must be one of:

Optio

n Meaning

N (Nomatch) Return the position of the first character in string that isn't

found in lookfor, or 0 if all of the characters in string also exist in

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lookfor.

M

(Match) Return the position of the first character in string that also

exists in lookfor, or 0 none of the characters in string also exist in

lookfor.

If omitted, option defaults to 'N'.

Returns

A character position (where 1 is the first character instring).

Notes

It is not an error ifstartrefers to more characters than string actually contains.

Example:

Example Used Output

VERIFY('foobar', 'barfo') 2VERIFY('foobar', 'barfo', 'M') 2VERIFY('foobar', 'fob', 'N') 5VERIFY('foobar', 'barf', 'N', 3) 3VERIFY('foobar', 'barf', 'N', 4) 0

XRANGE

Creates a range of characters between a given start character and end character. The

range of characters is produced from the computer's character set.

Syntax:

newstring = XRANGE(start, end)

start is which character to start from. If omitted, the default is to start fromcharacter 0 ('00'x).

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end is which character to end at. If omitted, the default is to end at character255 ('ff'x).

Returns

A string that consists of all the characters fromstartthrough end, inclusive.

Notes

The actual representation of the output from XRANGE() depends on the character set

used by your computer.

If the value ofstartis larger than the value ofend, the output will wrap around fromffx to 00x. Ifstartorendis not a string containing exactly one character, this raises

a SYNTAX error.

Example:

Example Used Output

XRANGE('A', 'J') 'ABCDEFGHIJ'

XRANGE('FC'x) 'FCFDFEFF'x

XRANGE(, '05'x) '000102030405'x

XRANGE('FD'x, '04'x) 'FDFEFF0001020304'x

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ConclusionAstringis basically a sequence of characters that can be indexed. Thestringdatatype provides a

number of useful and powerful high level operations. All the operations of strings are discussed

above, all the syntax and examples helps us to understand the concept of operations on strings.

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References

www.cs.grinnell.edu/~rebelsky/Espresso/Readings/strings.html

www.cs.hmc.edu/~geoff/classes/hmc.cs070.200401/notes/strings.html

www.ezysoftware.com/ezyprolog/Prolog_Inference_Engine/Prolog.../String_o

perations/psp_cat_String_Operations.htm
http://www.cs.hmc.edu/~geoff/classes/hmc.cs070.200401/notes/strings.htmlhttp://www.cs.hmc.edu/~geoff/classes/hmc.cs070.200401/notes/strings.html

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