diff --git a/nemu/src/monitor/sdb/expr.c b/nemu/src/monitor/sdb/expr.c
index 6555d65..9adb8b9 100644
--- a/nemu/src/monitor/sdb/expr.c
+++ b/nemu/src/monitor/sdb/expr.c
@@ -20,15 +20,21 @@
  */
 #include <regex.h>
 
+#include <memory/vaddr.h>
 #include <limits.h>
 
 enum {
-  TK_NOTYPE = 256, TK_EQ,
-  TK_DEC,
+  TK_NOTYPE = 256,
+  TK_EQ,
+  TK_NEQ,
+  TK_AND,
+  
   TK_NEG,
-
-  /* TODO: Add more token types */
-
+  TK_DEC,
+  
+  TK_HEX,
+  TK_REG,
+  TK_DEREF,
 };
 
 static struct rule {
@@ -36,13 +42,11 @@ static struct rule {
   int token_type;
 } rules[] = {
 
-  /* TODO: Add more rules.
-   * Pay attention to the precedence level of different rules.
-   */
-
   {" +", TK_NOTYPE},    // spaces
   {"\\+", '+'},         // plus
   {"==", TK_EQ},        // equal
+  {"!=", TK_NEQ},       // not equal
+  {"&&", TK_AND},       // and
 
   {"-", '-'},           // sub
   {"\\*", '*'},         // mul
@@ -50,6 +54,9 @@ static struct rule {
   {"\\(", '('},         // (
   {"\\)", ')'},         // )
   {"[0-9]+", TK_DEC},   // dec number
+
+  {"0x[0-9a-fA-F]+", TK_HEX}, // hex number
+  {"$[0-9a-z]+", TK_REG},     // register
 };
 
 #define NR_REGEX ARRLEN(rules)
@@ -113,9 +120,14 @@ static bool make_token(char *e) {
           case '/':
           case '(':
           case ')':
+          case TK_EQ:
+          case TK_NEQ:
+          case TK_AND:
             nr_token ++;
             break;
           case TK_DEC:
+          case TK_HEX:
+          case TK_REG:
             if (substr_len + 1 > sizeof(((Token*)0)->str)) {
               printf("token string is too long");
               return false;
@@ -124,7 +136,6 @@ static bool make_token(char *e) {
             tokens[nr_token].str[substr_len] = '\0';
             nr_token ++;
             break;
-          case TK_EQ:
           case TK_NOTYPE:
             break;
           default: TODO();
@@ -164,10 +175,14 @@ int check_parentheses(const Token* arr, size_t p, size_t q) {
 
 int get_level(int type) {
   switch (type) {
+    case TK_AND: return 1;
+    case TK_EQ:
+    case TK_NEQ: return 2;
     case '+':
-    case '-': return 1;
+    case '-': return 4;
     case '*':
-    case '/': return 2;
+    case '/': return 5;
+    case TK_DEREF: return 7;
     case TK_NEG: return 8;
     case '(': return 9;
     default: return INT_MAX;
@@ -196,7 +211,15 @@ uint32_t eval(const Token* arr, int p, int q, bool* success) {
      * For now this token should be a number.
      * Return the value of the number.
      */
-    return atoi(arr[q].str);
+    switch (arr[p].type)
+    {
+    case TK_DEC: return atoi(arr[q].str);
+    case TK_HEX: return strtol(arr[q].str, NULL, 16);
+    case TK_REG: return isa_reg_str2val(arr[q].str, success);
+    default:
+      *success = false;
+      break;
+    }
   }
   /* We should do more things here. */
   int op = 0;
@@ -220,6 +243,9 @@ uint32_t eval(const Token* arr, int p, int q, bool* success) {
       if (type == TK_NEG && type_level == op_type_level) {
         continue;
       }
+      if (type == TK_DEREF && type_level == op_type_level) {
+        continue;
+      }
       op = i;
       op_type_level = type_level;
     }
@@ -236,6 +262,10 @@ uint32_t eval(const Token* arr, int p, int q, bool* success) {
 
   switch (arr[op].type) {
     case TK_NEG: return - val_r;
+    case TK_DEREF: return vaddr_read(val_r, sizeof(word_t));
+    case TK_EQ: return val_l == val_r;
+    case TK_NEQ: return val_l != val_r;
+    case TK_AND: return val_l && val_r;
     case '+': return val_l + val_r;
     case '-': return val_l - val_r;
     case '*': return val_l * val_r;
@@ -244,25 +274,30 @@ uint32_t eval(const Token* arr, int p, int q, bool* success) {
   }
 }
 
+static inline bool prev_not_number(int i) {
+  return (i == 0 || \
+          tokens[i-1].type == '(' || \
+          tokens[i-1].type == '+' || \
+          tokens[i-1].type == '-' || \
+          tokens[i-1].type == '*' || \
+          tokens[i-1].type == '/' || \
+          tokens[i-1].type == TK_NEG || \
+          tokens[i-1].type == TK_DEREF);
+}
+
 word_t expr(char *e, bool *success) {
   if (!make_token(e)) {
     *success = false;
     return 0;
   }
 
-  /* TODO: Insert codes to evaluate the expression. */
-  // TODO();
   *success = true;
   for (int i = 0; i < nr_token; i ++) {
     int type = tokens[i].type;
-    if (type == '-' && (i == 0 || \
-                        tokens[i-1].type == '(' || \
-                        tokens[i-1].type == '+' || \
-                        tokens[i-1].type == '-' || \
-                        tokens[i-1].type == '*' || \
-                        tokens[i-1].type == '/' || \
-                        tokens[i-1].type == TK_NEG)) {
+    if (type == '-' && prev_not_number(i)) {
       tokens[i].type = TK_NEG;
+    } else if (type == '*' && prev_not_number(i)) {
+      tokens[i].type = TK_DEREF;
     }
   }
   return eval(tokens, 0, nr_token - 1, success);
diff --git a/nemu/src/monitor/sdb/sdb.c b/nemu/src/monitor/sdb/sdb.c
index 01f6267..62d607c 100644
--- a/nemu/src/monitor/sdb/sdb.c
+++ b/nemu/src/monitor/sdb/sdb.c
@@ -17,9 +17,10 @@
 #include <cpu/cpu.h>
 #include <readline/readline.h>
 #include <readline/history.h>
-#include <memory/vaddr.h>
 #include "sdb.h"
 
+#include <memory/vaddr.h>
+
 static int is_batch_mode = false;
 
 void init_regex();
diff --git a/nemu/tools/gen-expr/gen-expr.c b/nemu/tools/gen-expr/gen-expr.c
index 9234f1c..d4b6e7e 100644
--- a/nemu/tools/gen-expr/gen-expr.c
+++ b/nemu/tools/gen-expr/gen-expr.c
@@ -91,7 +91,7 @@ int main(int argc, char *argv[]) {
     fputs(code_buf, fp);
     fclose(fp);
 
-    int ret = system("gcc /tmp/.code.c -o /tmp/.expr");
+    int ret = system("gcc /tmp/.code.c -o /tmp/.expr -Wall -Werror");
     if (ret != 0) {
       printf("failed to execute gcc\n");
       i ++;