diff --git a/hw4/include/program.h b/hw4/include/program.h
new file mode 100644
index 0000000..f72df4a
--- /dev/null
+++ b/hw4/include/program.h
@@ -0,0 +1,14 @@
+typedef struct prog_data
+{
+    STMT *stmt;
+    struct prog_data *prev;
+    struct prog_data *next;
+} prog_data;
+
+prog_data *prog_head;
+prog_data *prog_counter;
+
+void prog_init();
+void prog_fini();
+prog_data *prog_get_data(int lineno);
+void prog_remove_data(prog_data* data);
diff --git a/hw4/include/store.h b/hw4/include/store.h
index 275fabd..b460195 100644
--- a/hw4/include/store.h
+++ b/hw4/include/store.h
@@ -6,7 +6,7 @@ typedef struct store_data
     struct store_data *next;
 } store_data;
 
-store_data *head;
+store_data *store_head;
 
 void store_init();
 store_data* store_get_data(char* var);
diff --git a/hw4/src/jobs.c b/hw4/src/jobs.c
index 19ec671..87573b8 100644
--- a/hw4/src/jobs.c
+++ b/hw4/src/jobs.c
@@ -12,6 +12,7 @@
 #include "mush.h"
 #include "debug.h"
 #include "store.h"
+#include "program.h"
 
 /*
  * This is the "jobs" module for Mush.
@@ -49,6 +50,7 @@
  */
 int jobs_init(void) {
     store_init();
+    prog_init();
     return 0;
 }
 
@@ -63,7 +65,9 @@ int jobs_init(void) {
  * @return 0 if finalization is completely successful, otherwise -1.
  */
 int jobs_fini(void) {
+    // TODO cancel jobs, wait for terminate
     store_fini();
+    prog_fini();
     return 0;
 }
 
@@ -85,7 +89,7 @@ int jobs_fini(void) {
  */
 int jobs_show(FILE *file) {
     // TO BE IMPLEMENTED
-    abort();
+    return 0;
 }
 
 /**
diff --git a/hw4/src/main.c b/hw4/src/main.c
index ca5b15a..364248b 100644
--- a/hw4/src/main.c
+++ b/hw4/src/main.c
@@ -5,6 +5,7 @@
 
 #include "mush.h"
 #include "store.h"
+#include "program.h"
 
 int main(int argc, char *argv[]) {
     jobs_init();
diff --git a/hw4/src/program.c b/hw4/src/program.c
index e6379b3..30ed82c 100644
--- a/hw4/src/program.c
+++ b/hw4/src/program.c
@@ -3,6 +3,7 @@
 
 #include "mush.h"
 #include "debug.h"
+#include "program.h"
 
 /*
  * This is the "program store" module for Mush.
@@ -25,8 +26,17 @@
  * @return  0 if successful, -1 if any error occurred.
  */
 int prog_list(FILE *out) {
-    // TO BE IMPLEMENTED
-    abort();
+    prog_data *ptr = prog_head->next;
+    while (1)
+    {
+        if (ptr == prog_counter)
+            fprintf(out, "-->\n");
+        if (ptr == prog_head)
+            break;
+        show_stmt(out, ptr->stmt);
+        ptr = ptr->next;
+    }
+    return 0;
 }
 
 /**
@@ -47,8 +57,30 @@ int prog_list(FILE *out) {
  * @return  0 if successful, -1 if any error occurred.
  */
 int prog_insert(STMT *stmt) {
-    // TO BE IMPLEMENTED
-    abort();
+    // if no lineno, return -1
+    if (!stmt->lineno)
+        return -1;
+
+    // get first stmt after lineno
+    prog_data *ptr = prog_get_data(stmt->lineno);
+
+    // if stmt exists
+    if (ptr != prog_head && ptr->stmt->lineno == stmt->lineno)
+    {
+        free_stmt(ptr->stmt);
+        ptr->stmt = stmt;
+        return 0;
+    }
+    
+
+    // insert the new one
+    prog_data *new = malloc(sizeof(prog_data));
+    new->next = ptr;
+    new->prev = ptr->prev;
+    new->prev->next = new;
+    new->next->prev = new;
+    new->stmt = stmt;
+    return 0;
 }
 
 /**
@@ -69,8 +101,24 @@ int prog_insert(STMT *stmt) {
  * @param max  Upper end of the range of line numbers to be deleted.
  */
 int prog_delete(int min, int max) {
-    // TO BE IMPLEMENTED
-    abort();
+    // get the stmt greater than or equal to min
+    prog_data *ptr = prog_get_data(min);
+
+    // deletion
+    while (1)
+    {
+        // break if next stmt is head or greater than max
+        if (ptr == prog_head || ptr->stmt->lineno > max)
+            break;
+        // if is counter, counter move to the next stmt
+        if (ptr == prog_counter)
+            prog_counter = ptr->next;
+        // delete statement
+        ptr = ptr->next;
+        prog_remove_data(ptr->prev);
+    }
+    
+    return 0;
 }
 
 /**
@@ -79,8 +127,7 @@ int prog_delete(int min, int max) {
  * before the first statement in the program.
  */
 void prog_reset(void) {
-    // TO BE IMPLEMENTED
-    abort();
+    prog_counter = prog_head->next;
 }
 
 /**
@@ -95,8 +142,9 @@ void prog_reset(void) {
  * counter position, if any, otherwise NULL.
  */
 STMT *prog_fetch(void) {
-    // TO BE IMPLEMENTED
-    abort();
+    if (prog_counter != prog_head)
+        return prog_counter->stmt;
+    return NULL;
 }
 
 /**
@@ -111,8 +159,11 @@ STMT *prog_fetch(void) {
  * position, if any, otherwise NULL.
  */
 STMT *prog_next() {
-    // TO BE IMPLEMENTED
-    abort();
+    // if has next
+    if (prog_counter != prog_head)
+        prog_counter = prog_counter->next;
+    
+    return prog_fetch();
 }
 
 /**
@@ -131,6 +182,53 @@ STMT *prog_next() {
  * statement exists, otherwise NULL.
  */
 STMT *prog_goto(int lineno) {
-    // TO BE IMPLEMENTED
-    abort();
+    // get first stmt with greter than or equal to lineno
+    prog_data *ptr = prog_get_data(lineno);
+    // return NULL is no such stmt exists
+    if (ptr == prog_head)
+        return NULL;
+    // if equal, return stmt
+    if (ptr->stmt->lineno == lineno) {
+        prog_counter = ptr;
+        return ptr->stmt;
+    }
+    // else return NULL
+    return NULL;
 }
+
+prog_data *prog_get_data(int lineno) {
+    // go through the double-linked list and find the fist stmt with lineno greater than or equal to lineno
+    prog_data *ptr = prog_head->next;
+    while (ptr != prog_head)
+    {
+        if (ptr->stmt->lineno >= lineno)
+            return ptr;
+        ptr = ptr->next;
+    }
+    return prog_head;
+}
+
+void prog_remove_data(prog_data* data) {
+    data->prev->next = data->next;
+    data->next->prev = data->prev;
+    if (data->stmt) {
+        free_stmt(data->stmt);
+    }
+    free(data);
+}
+
+void prog_init() {
+    prog_head = malloc(sizeof(prog_data));
+    prog_head->next = prog_head;
+    prog_head->prev = prog_head;
+    prog_head->stmt = NULL;
+    prog_counter = prog_head;
+}
+
+void prog_fini() {
+    while (prog_head->next != prog_head)
+        prog_remove_data(prog_head->next);
+
+    free(prog_head);
+    prog_head = NULL;
+}
\ No newline at end of file
diff --git a/hw4/src/store.c b/hw4/src/store.c
index aca225e..0bbf047 100644
--- a/hw4/src/store.c
+++ b/hw4/src/store.c
@@ -191,14 +191,14 @@ int store_set_int(char *var, long val) {
  * @param f  The stream to which the store contents are to be printed.
  */
 void store_show(FILE *f) {
-    store_data* ptr = head->next;
+    store_data* ptr = store_head->next;
 
     fprintf(f, "{");
-    while (ptr != head)
+    while (ptr != store_head)
     {
         fprintf(f, "%s=%s", ptr->name, ptr->value);
         ptr = ptr->next;
-        if ((ptr != head))
+        if ((ptr != store_head))
             fprintf(f, ", ");
         
     }
@@ -206,17 +206,17 @@ void store_show(FILE *f) {
 }
 
 void store_init() {
-    head = malloc(sizeof(store_data));
-    head->name = NULL;
-    head->value = NULL;
-    head->next = head;
-    head->prev = head;
+    store_head = malloc(sizeof(store_data));
+    store_head->name = NULL;
+    store_head->value = NULL;
+    store_head->next = store_head;
+    store_head->prev = store_head;
 }
 
 store_data* store_get_data(char* var) {
-    store_data* ptr = head->next;
+    store_data* ptr = store_head->next;
 
-    while (ptr != head)
+    while (ptr != store_head)
     {
         if (strcmp(ptr->name, var) == 0)
             return ptr;
@@ -238,18 +238,18 @@ void store_remove_data(store_data* data) {
 }
 
 void store_add_data(store_data* data) {
-    data->next = head->next;
-    data->prev = head;
+    data->next = store_head->next;
+    data->prev = store_head;
     data->next->prev = data;
     data->prev->next = data;
 }
 
 void store_fini() {
-    while (head->next != head)
-        store_remove_data(head->next);
+    while (store_head->next != store_head)
+        store_remove_data(store_head->next);
 
-    free(head);
-    head = NULL;
+    free(store_head);
+    store_head = NULL;
 }
 
 char* store_strcpy(char *str) {