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Ex.No: 13
Implementation Of Lexical Analyser Using Lex Tool
AIM:
To write a lex program to implement the lexical analyzer.
ALGORITHM:
1. Start the program
2. Open a file file.c in read and include the yylex() tool for
input scanning.
3. Define the alphabets and numbers.
4. Print the preprocessor, function, keyword using yytext.lex
tool.
5. Print the relational, assignment and all the operator using
yytext() tool.
6.
Also scan and print where the loop ends and begins.
7. Use yywrap() to enter an error.
8. Stop the program.
PROGRAM:
%{int COMMENT=0;
%}identifier [_a-zA-Z][_a-zA-Z0-9]*%%#.* {printf("\n%s is a
PREPROCESSOR DIRECTIVE",yytext);}int |float |char |while |for |do
|if |
break |continue |void |switch |case |long |struct |const
|typedef |return |
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else |goto {printf("\n\t%s is a KEYWORD",yytext);}"/*"
{COMMENT=1;
printf("\n\n\t COMMENT ENDS\n");}{identifier}\(
{if(!COMMENT)
printf("\n\nFUNCTION \n\t%s",yytext);}\{ {if(!COMMENT)
printf("\n BLOCK BEGINS");}\} {if(!COMMENT) printf("\n BLOCK
ENDS");}{identifier}(\[[0-9]*\])? {if(!COMMENT) printf("\n %s
IDENTIFIER",yytext);}\".*\" {if(!COMMENT) printf("\n %s is a
STRING",yytext);}[0-9]+ {if(!COMMENT) printf("\n %s is a
NUMBER",yytext);}\)(\;)? {if(!COMMENT) PRINTF("\N\T");ECHO;
printf("\n");}\( ECHO;= {if(!COMMENT) printf("\n\t%s is an
ASSIGNMENT OPERATOR",yytext);}\= |\< |== |\> {if(!COMMENT)
printf("\n\t%s is a RELATIONAL OPERATOR",yytext);}
|\n%%
int main(int argc,char **argv){if(argc > 1){FILE
*file;file=fopen(argv[1],"r");if(!file){
printf("could not open
%s\n",argv[1]);exit(0);}yyin=file;}yylex();printf("\n\n");return
0;}int yywrap(){
return 0;}
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INPUT (area.c):
#include#includedouble area_of_circle(double r);int main(int
argc,char *argv[]){if(argc < 2)
{printf("usage: %s radius\n",argv[0]);{exit(1);}else {double
radius=atof(argv[1]);double
area=area_of_circle(radius);printf("Area of circle with radius
%f=%f\n",radius,area);}return 0;
}
RESULT:
Thus the above the program is executed and the required output
is obtained.
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Ex.No: 14
Implementation Of Calculation Using Lex And Yacc
AIM:
To write a program to implement calculator using lex and
yacc.
ALGORITHM:
1. Start the program.
2. Perform the calculation using both the lex and yacc.
3. In the lex tool, if the given expression contains numbers and
letters then they are displayed
4. In the same way, the digits, letters and uminus are
identified and displayed using yacc
5. The calculation is performed and the result is displayed.
6. Stop the program.
PROGRAM:
USING LEX TOOL:
%{#include#include"y.tab.h"
int c;extern int
yylaval;%}%%"";[a-z]{c=yytext[0];yylaval=c-'a';return(LETTER);}[0-9]{c=yytext[0];yylaval=c-'0';return(DIGIT);}[a-z0-9/b]{c=yytext[0];return(c);}
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USING YACC TOOL:%{#includeint regs[26];int base;%}%start
list%token DIGIT
LETTER%left'|'%left'&'%left'+''-'%left'*''/''%'%left
UMINUS%%list:|list stat'\n'|list
error'\n'{yyerror();};stat:expr{printf("%d\n",$1);}|LETTER'='expr{regs[$1]=$3;};expr:'('expr')'{$$=$2;}|expr'*'expr{$$=$1*$3;}|
expr'/'expr{$$=$1/$3;}|expr'%'expr{$$=$1%$3;}|
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expr'+'expr{$$=$1+$3;}|expr'-'expr{$$=$1-$3;}|expr'&'expr{$$=$1&$3;}|expr'|'expr{$$=$1|$3;}
|'-'expr%prec UMINUS{$$=-$2;}|LETTER{$$=regs[$1];}|
number;number:DIGIT{$$=$1;base=($1==0)?8:10;}|number
DIGIT{$$=base*$1+$2;
}%%main(){return(yyparse());}yyerror(s)char*s;{fprintf(stderr,"%s\n",s);
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}yywrap(){return(1);}
OUTPUT:
RESULT:
Thus the above the program is executed and the required output
is obtained.
