Lex and Yacc Calculator code-Lex

%{  
 # include  
 # include "y.tab.h"  
 # include  
 %}  
 %%  
 [0-9]+(\.[0-9]+)? { yylval.dval=atof(yytext);return NUMBER;}  
 [\t] ; /* ignore whitespace */  
 \n {return 0;}  
 . return yytext[0];  
 %%  
 int yywrap(void)  
 {  
   return 1;  
 }

Lex and Yacc Calculator code-Yacc

 

 %{  
 # include  
 # include  
 %}  
 %union  
 {  
   double dval;  
 }  
 %token  NUMBER ;  
 %left '-''+'  
 %left '*''/'  
 %right '^'  
 %type  expr  
 %%  
 result:    
   '='expr   
   |expr {printf("%f",$1);}  
   ;  
 expr:  
   expr'+'expr {$$=$1+$3;}  
   | expr'-'expr {$$=$1-$3;}  
   | expr'*'expr {$$=$1*$3;}  
   | expr'^'expr   {  
       $$=pow($1,$3);}  
   | expr'/'expr {  
     if($3==0)  
       yyerror("devide by zero");  
     else  
       $$=$1/$3;}  
   | '-'expr   {$$=-$2;}  
   | '('expr')' { $$=$2;}  
   | NUMBER {$$=$1;}  
   ;  
 %%  
 void yyerror(char *s)  
 {  
   fprintf(stdout,"%s\n",s);  
 }  
 int main()  
 {  
   yyparse();  
   return 0;  
 }