Write a yacc program for calculator

The Lex specification has a rule to match a number and generate a token of type NUM which is actually the number 2. After I wrote the above specification for Lex, I realised that the tokenizer it defined deviates from the specification of the calculator which requires that any two consecutive tokens be separated by write a yacc program for calculator or more blank characters.

The parser need not be changed. How the specifications are structured and what each part contains in general is shortly described here. The input to the RPN calculator and the RPN expressions in particular can be defined by a rather simple grammar for Yacc, and Lex is well suited for translating the input into a sequence of tokens for that grammar.

January 31, at 5: In the Yacc specification we provide a main function for the generated C program. Below, we concentrate on how the input is scanned and parsed according to the grammatical rules presented. This is a good testimony of the value of separation.

C Program to Make a Simple Calculator Using switch...case

Once more, notice the convenience of dealing with scanning separately from parsing proper. By use of them the corresponding subexpressions are evaluated and their results propagated up to where the entire expression is finally matched and its result printed in line.

A line is either empty an end- of- line characteror an RPN expression, or something else. The main rule is responsible for parsing the input as a sequence of lines. Lex tool source is the table of regular expressions and corresponding program.

Matching error by definition yields calling the user- defined function yyerror, after which we invoke the special action yyerrok to suppress a further propagation of the state of error. Moreover, even in the case of a small program like our RPN calculator the gain in simplicity and clarity is obvious.

It has nothing to do except calling yyparse, but its presence ensures completeness of the program in the sense that no other code needs to be compiled and linked besides the two files generated by Lex and Yacc.

Blanks are skipped as in the previous version of the specification. The variable yytext is a string: To this end it recursively defines the category input as a possibly empty sequence of instances of the category line. YACC program for an infix calculator We will keep the same operators as the postfix calculator, but we will give them their usual associativity left.

Write a program to implement calculator using LEX and YACC

If it is not a number, but it consists of only one character, we pass that character as a self- represented token. Somehow, it came naturally as a consequence of the separation of scanning from parsing, and perhaps of the way Lex works.

It is consulted when the scanner encounters end of input. Note that I did not intend to implement this more general behaviour a feature, one might say. The other two rules prescribe that nonblank characters not matched as parts of numbers including the arithmetic operatorsas well as the end- of- line character, generate self- represented tokens, while series of blank characters generate nothing and thus remain unseen by the parser.

Implemented as above, the calculator accepts expressions even if some pairs of tokens are not separated by blanks, provided that they can be unambiguously split anyway. However, to achieve equivalence with the implementations in the other languages I present, I show another Lex specification.

This time, instead of explicitly defining the grammar of a number, we rely on the C library function strtod to tell if a string represents a number. The variable yyleng is provided by Lex and is the length of yytext. If a string of nonblank characters is a number, we pass a NUM token to the parser.

The overall size of these specifications is noticeably smaller than the program implementing the calculator directly in C, despite the overhead of things not specific to our problem in both Yacc and Lex parts. Returning 1 from yywrap causes the scanner yylex to return a 0, which signifies end of input to the parser yyparse as well.

Together, the two specifications shown below are the equivalent of a program implementing an RPN calculator, as they completely and inambiguously define the actual generated program. The rpn category matches an RPN expression and so is recursively defined:Before writing a compiler was a very time- consuming process.

Then Lesk [] and Johnson [] published papers on lex and yacc. These utilities greatly simplify compiler writing. A real English-language program would probably use this flex code to recognize parts of speech, combined with a yacc program to recognize the grammatical structure of the sentence.

chy and chl, the yacc and flex portions of a simple calculator program (copied from the O'Reilly book).

Example Program for the lex and yacc Programs. This section describes example programs for the lex and yacc commands. Together, these example programs create a simple, desk-calculator program that performs addition, subtraction, multiplication, and division operations. I am new to lex and yacc programs.I have been trying to write a yacc program which takes as input an arithmetic expression and gives prefix notation as output.

here is my lex code. %{ #include. Simple calculator compiler using Lex and YACC. Lex tool source is the table of regular expressions and corresponding program fragments.

With the help of YACC and Lex tool one can write. This section contains example programs for the lex and yacc commands. Together, these example programs create a simple, desk-calculator program that performs addition, subtraction, multiplication, and division operations.

Write a yacc program for calculator
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