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  1. %{
  2. #include <stdio.h>
  3. #include <stdlib.h>
  4.  
  5. int yylex(void);
  6. void yyerror(char *s);
  7. %}
  8.  
  9. %token NUMBER
  10. %left '+' '-'
  11. %left '*' '/'
  12. %left NEG
  13.  
  14. %%
  15.  
  16. expr:
  17.     expr '+' expr  { $$ = $1 + $3; }
  18.   | expr '-' expr  { $$ = $1 - $3; }
  19.   | expr '*' expr  { $$ = $1 * $3; }
  20.   | expr '/' expr  {
  21.                     if ($3 == 0) {
  22.                         yyerror("Error: Division by zero.");
  23.                         YYABORT;
  24.                     }
  25.                     $$ = $1 / $3; 
  26.                   }
  27.   | '(' expr ')'   { $$ = $2; }
  28.   | NUMBER         { $$ = $1; }
  29.   ;
  30.  
  31. %%
  32.  
  33. /* Lexical Analyzer (Flex section) */
  34.  
  35. %{
  36. #include "y.tab.h"
  37. %}
  38.  
  39. %%
  40. [0-9]+  { yylval = atoi(yytext); return NUMBER; }
  41. "+"     { return '+'; }
  42. "-"     { return '-'; }
  43. "*"     { return '*'; }
  44. "/"     { return '/'; }
  45. "("     { return '('; }
  46. ")"     { return ')'; }
  47. [ \t\n] { /* Ignore whitespace */ }
  48. .       { printf("Unexpected character: %s\n", yytext); return 0; }
  49. %%
  50.  
  51. /* Error handling */
  52. void yyerror(char *s) {
  53.     fprintf(stderr, "%s\n", s);
  54. }
  55.  
  56. int main(void) {
  57.     printf("Enter an arithmetic expression: ");
  58.     if (yyparse() == 0) {
  59.         printf("Valid arithmetic expression\n");
  60.     } else {
  61.         printf("Invalid arithmetic expression\n");
  62.     }
  63.     return 0;
  64. }
  65.  
Success #stdin #stdout #stderr 0.03s 6872KB
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stdin
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Standard input is empty
stdout
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Standard output is empty
stderr
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ERROR: /home/FsxVFU/prog:2:1: Syntax error: Operator expected
ERROR: /home/FsxVFU/prog:64:1: Syntax error: Unexpected end of file
ERROR: '$runtoplevel'/0: Undefined procedure: program/0
   Exception: (3) program ? EOF: exit
https://ideone.com/lu2B3u
language:
Prolog (swi 7.6.4)
created:
1 day ago
visibility:
public

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