add yacc programs

2 files changed, 56 insertions, 0 deletions

diff --git a/7/main.l b/7/main.l
new file mode 100644
index 0000000..7e1332f
--- /dev/null
+++ b/7/main.l
@@ -0,0 +1,22 @@
+%{
+#include "y.tab.h"
+extern int yylval;
+%}
+
+%%
+[0-9]+ {
+    yylval = atoi(yytext);
+    return NUM;
+}
+"+" return ADD;;
+"-" return SUB;
+"*" return MUL;
+"/" return DIV;
+"(" return LPAR;
+")" return RPAR;
+\n return 0;
+%%
+
+int yywrap() {
+    return 1;
+}
diff --git a/7/main.y b/7/main.y
new file mode 100644
index 0000000..26a2007
--- /dev/null
+++ b/7/main.y
@@ -0,0 +1,34 @@
+%{
+#include <stdio.h>
+#include <stdlib.h>
+int yylex();
+int yyerror(char *);
+%}
+
+%token NUM ADD SUB MUL DIV LPAR RPAR
+%left ADD SUB MUL DIV
+%right NEG
+
+%%
+
+S:
+ E { printf("\n"); };
+E:
+ E ADD E   { printf("+ "); }
+ | E MUL E { printf("* "); }
+ | E SUB E { printf("- "); }
+ | E DIV E { printf("/ "); }
+ | LPAR E RPAR
+ | SUB E %prec NEG { printf("- "); }
+ | NUM { printf("%d ", yylval); }
+ ;
+%%
+
+int main() {
+    yyparse();
+}
+
+int yyerror(char *s) {
+    printf("error: %s", s);
+    exit(0);
+}