3 files changed, 110 insertions, 0 deletions

diff --git a/11/input b/11/input
new file mode 100644
index 0000000..7e9718c
--- /dev/null
+++ b/11/input
@@ -0,0 +1 @@
+for(i=0;i!=20;i--){for(;;){for(;;)i=1;}}
diff --git a/11/main.l b/11/main.l
new file mode 100644
index 0000000..5cc2a4e
--- /dev/null
+++ b/11/main.l
@@ -0,0 +1,33 @@
+%{
+#include "y.tab.h"
+extern int yylval;
+%}
+
+%%
+"++" return INC;
+"--" return DEC;
+"+" return ADD;
+"-" return SUB;
+"*" return MUL;
+"/" return DIV;
+"=" return ASSIGN;
+"==" return EQ;
+"!=" return NEQ;
+"<" return LT;
+">" return GT;
+"<=" return LTE;
+">=" return GTE;
+";" return ENDL;
+"for" return FOR;
+[0-9]+ {
+    yylval = atoi(yytext);
+    return NUM;
+};
+[a-zA-Z_][a-zA-Z_0-9]* return ID;
+. return yytext[0];
+\n return 0;
+%%
+
+int yywrap() {
+    return 1;
+}
diff --git a/11/main.y b/11/main.y
new file mode 100644
index 0000000..9ed51a0
--- /dev/null
+++ b/11/main.y
@@ -0,0 +1,76 @@
+%{
+#include <stdio.h>
+#include <stdlib.h>
+#include "lex.yy.cc"
+int yylex();
+int yyerror(char *);
+int loop_count = 0;
+%}
+
+%token ADD SUB MUL DIV INC DEC
+%token LT GT LTE GTE EQ NEQ ASSIGN
+%token FOR
+%token ENDL
+%token NUM ID
+
+%start statement
+
+%%
+primary_expr: NUM
+            | ID
+            ;
+
+postfix_expr: postfix_expr INC
+            | postfix_expr DEC
+            | primary_expr
+            ;
+
+unary_expr: INC unary_expr
+          | DEC unary_expr
+          | postfix_expr
+          ;
+
+boolean_expr: unary_expr LT unary_expr
+            | unary_expr GT unary_expr
+            | unary_expr LTE unary_expr
+            | unary_expr GTE unary_expr
+            | unary_expr EQ unary_expr
+            | unary_expr NEQ unary_expr
+            ;
+
+assignment_expr: unary_expr ASSIGN unary_expr
+               | unary_expr ASSIGN boolean_expr
+               ;
+
+expression: unary_expr
+          | boolean_expr
+          | assignment_expr
+          ;
+
+block: '{' statement block_cont
+     ;
+block_cont: statement block_cont
+          | '}'
+          ;
+
+statement: expression ENDL
+         | block
+         | for_expr {loop_count++;}
+         | ENDL
+         ;
+
+for_expr: FOR '(' statement statement expression ')' statement
+        | FOR '(' statement statement ')' statement
+        ;
+
+%%
+
+int main() {
+    yyparse();
+    printf("valid expression, nested %d", loop_count);
+}
+
+int yyerror(char *s) {
+    printf("error: %s", s);
+    exit(0);
+}