Lex and Yacc Learn (vi) the Lex & Yacc (Simple calculator program) runs

Lexical analysis program CH3-01.L

%{
#include "ch3-01.tab.h"
extern int yylval;
%}

percent
(0-9]+	{yylval = Atoi (yytext); return number;}
[\ t]	;		/* Ignore white space */
\ n	return 0;	/* Logical EOF */
.	return yytext[0];
%%

CH3-01.Y Syntax Analysis program

%token name number
percent
statement:	name ' = ' Expression
	|	Expression		{printf ("=%d\n", $);}
	;

Expression:	expression ' + ' number	{$$ = $ + $;}
	|	Expression '-' number	{$$ = $-$;}
	|	Number			{$$ = $;}
	;
Percent of
int main ()
{
	yyparse ();
	return 0;
}

int Yyerror (char *s)
{
	printf ("%s/n", s);
	return 0;
}

compile Run command:

(1) First, compile the lex file, generate the Lex.yy.c file

Flex CH3-01.L

(2) Second, compile the Yacc file, generate Ch3-01.tab.h and CH3-01.TAB.C files

Bison-d CH3-01.Y

(3) Link the generated. c file and generate the appropriate executable file

Gcc-o ch3-01 CH3-01.TAB.C LEX.YY.C-LY-LFL

(4) Run the executable file to calculate a simple expression

./ch3-01.exe

99+11