Encyclopedia of Computer Science and Technology

82 characters and stringsAs computer use became more widespread internationally,even 256 characters proved to be inadequate. A newstandard called Unicode can accommodate all of the world’salphabetic languages including Arabic, Hebrew, and Japanese(Kana Unicode schemes can also be used to encodeideographic languages (such as Chinese) and languagessuch as Korean that use syllabic components. At presenteach ideograph has its own character code, but Unicode 3.0includes a scheme for describing ideographs through theircomponent parts (radicals). Most modern operating systemsuse Unicode exclusively for character representation. However,support in software such as Web browsers is far fromcomplete, though steadily improving. Unicode also includesmany sets of internationally used symbols such as thoseused in mathematics and science. In order to accommodatethis wealth of characters, Unicode uses 16 bits to store eachcharacter, allowing for 65,535 different characters at theexpense of requiring twice the memory storage.Programming with StringsBefore considering how characters are actually manipulatedin the computer, it is important to realize that what thebinary value such as 1000001 (decimal 65) stored in a byteof memory actually represents depends on the context givento it by the program accessing that location. If the programdeclares an integer variable, then the data is numeric. If theprogram declares a character (char) value, then the data willbe interpreted as an uppercase “A” (in the ASCII system).Most character data used by programs actually representswords, sentences, or longer pieces of text. Multiplecharacters are represented as a string. For example, in traditionalBASIC the statement:NAME$ = “Homer Simpson”declares a string variable called NAME$ (the $ is a suffixindicating a string) and sets its value to the character string“Homer Simpson.” (The quotation marks are not actuallystored with the characters.)Some languages (such as BASIC) store a string in memoryby first storing the number of characters in the string,followed by the characters, with one in each byte of memory.In the family of languages that includes C, however,there is no string type as such. Instead, a string is stored asan array of char. Thus, in C the preceding example mightlook like this:char Name [20] = “Homer Simpson”;This declares Name as an array of up to 20 characters, andinitializes it to the string literal “Homer Simpson.”An alternative (and equivalent) form is:char * Name = “Homer Simpson”;Here Name is a pointer that returns the memory locationwhere the data begins. The string of characters “HomerSimpson” is stored starting at that location.Unlike the case with BASIC, in the C languages, thenumber of characters is not stored at the beginning of thedata. Rather, a special “null” character is stored to mark theend of the string.Programs can test strings for equality or even for greaterthan or less than. However, programmers must be carefulto understand the collating sequence, or the order given tocharacters in a character set such as ASCII. For example thetestIf State = “CA”will fail if the current value of State is “ca.” The lowercasecharacters have different numeric values than their uppercasecounterparts (and indeed must, if the two are to bedistinguished). Similarly, the expression:“Zebra” < “aardvark”is true because uppercase Z comes before lowercase “a” inthe collating sequence.Programming languages differ considerably in theirfacilities for manipulating strings. BASIC includes built-infunctions for determining the length of a string (LEN) andfor extracting portions of a string (substrings). For examplegiven the string Test consisting of the text “Test Data,” theexpression Right$ (Test, 4) would return “data.”Following their generally minimalist philosophy, theC and C++ languages contains no string facilities. Rather,they are provided as part of the standard library, which canbe included in programs as needed. In the following littleprogram:#include #include void main (){char String1[20];char String2[20];strcpy (String1, “Homer”);strcpy (String2, “Simpson”);//Concatenate string2 to the end of string1strcat (String1, String2);cout String1