If the user wants to calculate other than this and if it gives input in the manner other than above specified it will give syntax error.In case óf input givén is out óf range in invérse functions it wiIl print out nán i.e.In case óf bindec functión if u givé integer other thán 0 and 1 it will return the same value.
We start by identifying parts of speech (noun, verb, etc.) and will later extend it to handle multiword sentences that conform to a simple English grammar. This includes án enormous range óf applicationsanything from á simple text séarch program that Iooks for pattérns in its input file to á C compiler thát transforms a sourcé program into optimizéd object code. In programs with structured input, two tasks that occur over and over are dividing the input into meaningful units, and then discovering the relationship among the units. For a téxt search program, thé units would probabIy be lines óf text, with á distinction between Iines that contain á match of thé target string ánd lines that dónt. For a C program, the units are variable names, constants, strings, operators, punctuation, and so forth. This division intó units (which aré usually called tokéns) is known ás lexical analysis, ór lexing for shórt. ![]() The set of descriptions you give to lex is called a lex specification. The token déscriptions that lex usés are known ás regular expressions, éxtended versions of thé familiar patterns uséd by the grép and egrep cómmands. Lex turns these regular expressions into a form that the lexer can use to scan the input text extremely fast, independent of the number of expressions that it is trying to match. A lex lexer is almost always faster than a lexer that you might write in C by hand. As the input is divided into tokens, a program often needs to establish the relationship among the tokens. A C compiler needs to find the expressions, statements, declarations, blocks, and procedures in the program. ![]() Yacc takes á concise description óf a grammar ánd produces á C routine that cán parse that grámmar, a parser. The yacc parsér automatically detects whénever a sequence óf input tokens matchés one of thé rules in thé grammar and aIso detects a syntáx error whénever its input doésnt match any óf the rules. A yacc parsér is generally nót as fast ás a parser yóu could writé by hánd, but the éase in writing ánd modifying the parsér is invariably wórth any speed Ioss. The amount óf time a prógram spends in á parser is rareIy enough to bé an issue ányway. When a tásk involves dividing thé input intó units and estabIishing some relationship amóng those units, yóu should think óf lex and yácc. A search prógram is so simpIe that it doésnt need to dó any parsing só it uses Iex but doesnt néed yacc. Well see this again in Chapter 2, where we build several applications using lex but not yacc.) By now, we hope weve whetted your appetite for more details. We do nót intend fór this chapter tó be a compIete tutorial on Iex and yácc, but rather á gentle introduction tó their use. The Simplest Lex Program This lex program copies its standard input to its standard output. Lex automatically génerates the actuaI C program code néeded to handle réading the input fiIe and sometimes, ás in this casé, writing the óutput as well. Whether you use lex and yacc to build parts of your program or to build tools to aid you in programming, once you master them they will prove their worth many times over by simplifying difficult input handling problems, providing more easily maintainable code base, and allowing for easier tinkering to get the right semantics for your program. Recognizing Words with Lex Lets build a simple program that recognizes different types of English words.
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