diff --git a/Makefile b/Makefile
index 5f52207..c241ba1 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 CC = gcc
-CFLAGS = -Wall -Wextra -g
+CFLAGS = -Wall -Wextra -g -std=c11 -D_POSIX_C_SOURCE=200809L
 LDFLAGS =
 SRCS = forth_core.c forth_dict.c forth_words.c forth_interp.c main.c
 OBJS = $(SRCS:.c=.o)
diff --git a/README.md b/README.md
index 75f9691..8d7b573 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,7 @@ This is a toy/subset Forth interpreter designed for educational purposes. It pro
 
 - **Threaded Code**: The interpreter uses an inner/outer interpreter model. Colon definitions are sequences of word addresses (threaded code) traversed by an instruction pointer.
 - **Architecture**: 
-  - 32-bit signed integer cells (`int32_t`)
+  - 64-bit signed integer cells (`int64_t`)
   - Separate data and return stacks
   - Fixed-size dictionary, user memory, and compile buffer
   - Dictionary is a singly-linked list searched linearly
@@ -23,8 +23,8 @@ This is a toy/subset Forth interpreter designed for educational purposes. It pro
   - Memory access (`@`, `!`, `C@`, `C!`, `HERE`, `ALLOT`)
   - Simple string output (`."`)
 - **Limitations**:
-  - Fixed memory limits (dictionary, stacks, user memory)
-  - 32-bit signed integers only; no floating-point support
+  - Fixed user memory limit (1M cells); dictionary and stacks grow dynamically
+  - 64-bit signed integers only; no floating-point support
   - No file I/O or operating system interface beyond stdin/stdout
   - No immediate user-defined words or advanced introspection
   - Single-threaded execution
diff --git a/forth.h b/forth.h
index b0ab712..56b6ab6 100644
--- a/forth.h
+++ b/forth.h
@@ -7,10 +7,14 @@
 #include <ctype.h>
 #include <stdint.h>
 #include <inttypes.h>
+#include <sys/types.h>
 
 // Configuration (all hard limits removed)
 #define MAX_NAME_LEN 31
 
+#define F_IMMEDIATE (1 << 7)
+#define F_HIDDEN    (1 << 6)
+
 // Core types
 typedef struct Word Word;
 typedef union Cell {
@@ -45,7 +49,8 @@ extern int32_t compile_idx;
 extern int32_t compile_cap;
 extern char compiling_name[MAX_NAME_LEN + 1];
 
-extern char input_buf[1024];      // fixed for line input
+extern char* input_buf;           // line buffer (dynamic, managed by getline)
+extern size_t input_buf_cap;
 extern char* input_ptr;
 
 extern int64_t *compile_stack;    // holds indices into compile_buf
@@ -56,6 +61,14 @@ extern Cell *user_mem;
 extern int64_t user_mem_size;     // in cells
 extern Cell* here;
 
+// Pointers to critical hidden/primitive words (set during init)
+extern Word* w_exit;
+extern Word* w_docolon;
+extern Word* w_lit;
+extern Word* w_branch;
+extern Word* w_zbranch;
+extern Word* w_dot_quote_inner;
+
 // Core function prototypes
 void data_push(int64_t val);
 int64_t data_pop(void);
diff --git a/forth_core.c b/forth_core.c
index 29f5fa1..a7adc58 100644
--- a/forth_core.c
+++ b/forth_core.c
@@ -18,7 +18,8 @@ int32_t compile_idx = 0;
 int32_t compile_cap = 0;
 char compiling_name[MAX_NAME_LEN + 1] = {0};
 
-char input_buf[1024] = {0};
+char* input_buf = NULL;
+size_t input_buf_cap = 0;
 char* input_ptr = NULL;
 
 int64_t *compile_stack = NULL;
@@ -29,6 +30,13 @@ Cell *user_mem = NULL;
 int64_t user_mem_size = 0;
 Cell* here = NULL;
 
+Word* w_exit = NULL;
+Word* w_docolon = NULL;
+Word* w_lit = NULL;
+Word* w_branch = NULL;
+Word* w_zbranch = NULL;
+Word* w_dot_quote_inner = NULL;
+
 // ---------- Data stack ----------
 void data_push(int64_t val) {
     if (data_sp + 1 >= data_cap) {
diff --git a/forth_interp.c b/forth_interp.c
index ee1ef63..980f0ec 100644
--- a/forth_interp.c
+++ b/forth_interp.c
@@ -73,13 +73,12 @@ void process_token(const char* token) {
             if (state == 0) {
                 data_push((int64_t)v);
             } else { // Compile lit + number
-                Word* lit_w = lookup_word_internal("lit");
-                if (!lit_w) {
+                if (!w_lit) {
                     fprintf(stderr, "Fatal: lit word not found\n");
                     return;
                 }
                 ensure_compile_cap(2);
-                compile_buf[compile_idx++] = (Cell){.word = lit_w};
+                compile_buf[compile_idx++] = (Cell){.word = w_lit};
                 compile_buf[compile_idx++] = (Cell){.num = (int64_t)v};
             }
         } else {
@@ -92,9 +91,13 @@ void outer_interpreter(void) {
     while (1) {
         printf("ok ");
         fflush(stdout);
-        if (fgets(input_buf, sizeof(input_buf), stdin) == NULL) {
+        ssize_t n = getline(&input_buf, &input_buf_cap, stdin);
+        if (n < 0) {
             break;
         }
+        if (n > 0 && input_buf[n - 1] == '\n') {
+            input_buf[n - 1] = '\0';
+        }
         input_ptr = input_buf;
         char* tok;
         while ((tok = next_token()) != NULL) {
diff --git a/forth_words.c b/forth_words.c
index e3e878d..3b7058c 100644
--- a/forth_words.c
+++ b/forth_words.c
@@ -60,10 +60,11 @@ void do_nip(Word* w) {
 void do_tuck(Word* w) {
     (void)w;
     if (data_sp < 1) return;
-    int64_t a = data_stack[data_sp-1];
-    int64_t b = data_stack[data_sp];
-    data_push(a);
-    data_stack[data_sp-2] = b;
+    int64_t x1 = data_stack[data_sp-1];
+    int64_t x2 = data_stack[data_sp];
+    data_stack[data_sp-1] = x2;
+    data_stack[data_sp] = x1;
+    data_push(x2);
 }
 
 // Arithmetic
@@ -97,7 +98,7 @@ void do_div(Word* w) {
     int64_t b = data_pop();
     int64_t a = data_pop();
     if (b == 0) {
-        printf("Division by zero\n");
+        fprintf(stderr, "Division by zero\n");
         data_push(a);
         data_push(b);
         return;
@@ -111,7 +112,7 @@ void do_mod(Word* w) {
     int64_t b = data_pop();
     int64_t a = data_pop();
     if (b == 0) {
-        printf("Modulo by zero\n");
+        fprintf(stderr, "Modulo by zero\n");
         data_push(a);
         data_push(b);
         return;
@@ -125,7 +126,7 @@ void do_slash_mod(Word* w) {
     int64_t b = data_pop();
     int64_t a = data_pop();
     if (b == 0) {
-        printf("Modulo by zero\n");
+        fprintf(stderr, "Modulo by zero\n");
         data_push(a);
         data_push(b);
         return;
@@ -335,30 +336,29 @@ void do_dot_quote(Word* w) {
     (void)w;
     if (state == 0) {
         // Interpret mode: print immediately
-        if (input_ptr == NULL) { printf("Missing string\n"); return; }
+        if (input_ptr == NULL) { fprintf(stderr, "Missing string\n"); return; }
         while (*input_ptr && isspace((unsigned char)*input_ptr)) input_ptr++;
-        if (*input_ptr != '"') { printf("Expected \" to start string\n"); return; }
+        if (*input_ptr != '"') { fprintf(stderr, "Expected \" to start string\n"); return; }
         input_ptr++;
         char* start = input_ptr;
         while (*input_ptr && *input_ptr != '"') input_ptr++;
-        if (*input_ptr != '"') { printf("Unterminated string\n"); return; }
+        if (*input_ptr != '"') { fprintf(stderr, "Unterminated string\n"); return; }
         while (start < input_ptr) putchar(*start++);
         input_ptr++;
         fflush(stdout);
     } else {
         // Compile mode: compile string for runtime
-        if (input_ptr == NULL) { printf("Missing string\n"); return; }
+        if (input_ptr == NULL) { fprintf(stderr, "Missing string\n"); return; }
         while (*input_ptr && isspace((unsigned char)*input_ptr)) input_ptr++;
-        if (*input_ptr != '"') { printf("Expected \" to start string\n"); return; }
+        if (*input_ptr != '"') { fprintf(stderr, "Expected \" to start string\n"); return; }
         input_ptr++;
         char* start = input_ptr;
         while (*input_ptr && *input_ptr != '"') input_ptr++;
-        if (*input_ptr != '"') { printf("Unterminated string\n"); return; }
+        if (*input_ptr != '"') { fprintf(stderr, "Unterminated string\n"); return; }
         size_t len = input_ptr - start;
-        Word* inner_w = lookup_word_internal("do_dot_quote_inner");
-        if (!inner_w) { printf("Fatal: do_dot_quote_inner not found\n"); return; }
+        if (!w_dot_quote_inner) { fprintf(stderr, "Fatal: do_dot_quote_inner not found\n"); return; }
         ensure_compile_cap(2 + (int32_t)len);
-        compile_buf[compile_idx++] = (Cell){.word = inner_w};
+        compile_buf[compile_idx++] = (Cell){.word = w_dot_quote_inner};
         compile_buf[compile_idx++] = (Cell){.num = (int64_t)len};
         for (size_t i = 0; i < len; i++) {
             compile_buf[compile_idx++] = (Cell){.num = (int64_t)start[i]};
@@ -394,7 +394,7 @@ void do_fetch(Word* w) {
     (void)w;
     int64_t addr = data_pop();
     if (addr < 0 || addr >= user_mem_size) {
-        printf("Address out of bounds\n");
+        fprintf(stderr, "Address out of bounds\n");
         return;
     }
     data_push(user_mem[addr].num);
@@ -405,7 +405,7 @@ void do_store(Word* w) {
     int64_t addr = data_pop();
     int64_t val = data_pop();
     if (addr < 0 || addr >= user_mem_size) {
-        printf("Address out of bounds\n");
+        fprintf(stderr, "Address out of bounds\n");
         return;
     }
     user_mem[addr].num = val;
@@ -416,7 +416,7 @@ void do_plus_store(Word* w) {
     int64_t addr = data_pop();
     int64_t val = data_pop();
     if (addr < 0 || addr >= user_mem_size) {
-        printf("Address out of bounds\n");
+        fprintf(stderr, "Address out of bounds\n");
         return;
     }
     user_mem[addr].num += val;
@@ -427,7 +427,7 @@ void do_cfetch(Word* w) {
     int64_t addr = data_pop();   // byte offset
     int64_t max_byte = user_mem_size * (int64_t)sizeof(Cell);
     if (addr < 0 || addr >= max_byte) {
-        printf("Address out of bounds\n");
+        fprintf(stderr, "Address out of bounds\n");
         return;
     }
     uint8_t* base = (uint8_t*)user_mem;
@@ -440,7 +440,7 @@ void do_cstore(Word* w) {
     int64_t val = data_pop();
     int64_t max_byte = user_mem_size * (int64_t)sizeof(Cell);
     if (addr < 0 || addr >= max_byte) {
-        printf("Address out of bounds\n");
+        fprintf(stderr, "Address out of bounds\n");
         return;
     }
     uint8_t* base = (uint8_t*)user_mem;
@@ -457,7 +457,7 @@ void do_allot(Word* w) {
     (void)w;
     int64_t n = data_pop();
     if (here + n > user_mem + user_mem_size) {
-        printf("User memory overflow\n");
+        fprintf(stderr, "User memory overflow\n");
         return;
     }
     here += n;
@@ -467,11 +467,11 @@ void do_allot(Word* w) {
 void do_variable(Word* w) {
     (void)w;
     char* name = next_token();
-    if (!name) { printf("VARIABLE expects a name\n"); return; }
+    if (!name) { fprintf(stderr, "VARIABLE expects a name\n"); return; }
 
     // allocate one cell in user memory for the variable's data
     if (here + 1 > user_mem + user_mem_size) {
-        printf("User memory overflow\n");
+        fprintf(stderr, "User memory overflow\n");
         return;
     }
     Cell* var_cell = here;    // address of the data cell
@@ -497,11 +497,11 @@ void do_constant(Word* w) {
     (void)w;
     int64_t val = data_pop();
     char* name = next_token();
-    if (!name) { printf("CONSTANT expects a name\n"); data_push(val); return; }
+    if (!name) { fprintf(stderr, "CONSTANT expects a name\n"); data_push(val); return; }
 
     // allocate a cell in user memory to hold the constant value
     if (here + 1 > user_mem + user_mem_size) {
-        printf("User memory overflow\n");
+        fprintf(stderr, "User memory overflow\n");
         data_push(val);       // restore the value (optional)
         return;
     }
@@ -547,7 +547,7 @@ void do_r_from(Word* w) {
 
 void do_r_fetch(Word* w) {
     (void)w;
-    if (rp < 0) { printf("Return stack underflow\n"); return; }
+    if (rp < 0) { fprintf(stderr, "Return stack underflow\n"); return; }
     data_push(ret_stack[rp].num);
 }
 
@@ -572,7 +572,7 @@ void do_lit(Word* w) {
 void do_colon(Word* w) {
     (void)w;
     char* name = next_token();
-    if (!name) { printf("':' expects a name\n"); return; }
+    if (!name) { fprintf(stderr, "':' expects a name\n"); return; }
     size_t len = strlen(name);
     if (len > MAX_NAME_LEN) len = MAX_NAME_LEN;
     memcpy(compiling_name, name, len);
@@ -584,12 +584,11 @@ void do_colon(Word* w) {
 
 void do_semicolon(Word* w) {
     (void)w;
-    if (state != 1) { printf("';' only valid in compile mode\n"); return; }
-    Word* exit_w = lookup_word("exit");
-    if (!exit_w) { printf("Fatal: exit word not found\n"); return; }
+    if (state != 1) { fprintf(stderr, "';' only valid in compile mode\n"); return; }
+    if (!w_exit) { fprintf(stderr, "Fatal: exit word not found\n"); return; }
 
     ensure_compile_cap(1);
-    compile_buf[compile_idx++] = (Cell){.word = exit_w};
+    compile_buf[compile_idx++] = (Cell){.word = w_exit};
 
     // Create body copy of compiled cells
     Cell* body_copy = malloc(compile_idx * sizeof(Cell));
@@ -633,11 +632,10 @@ void do_zero_branch(Word* w) {
 // Control flow using compile stack (indices)
 void do_if(Word* w) {
     (void)w;
-    if (state != 1) { printf("IF only valid in compile mode\n"); return; }
-    Word* zbranch = lookup_word_internal("0branch");
-    if (!zbranch) { printf("Fatal: 0branch not found\n"); return; }
+    if (state != 1) { fprintf(stderr, "IF only valid in compile mode\n"); return; }
+    if (!w_zbranch) { fprintf(stderr, "Fatal: 0branch not found\n"); return; }
     ensure_compile_cap(2);
-    compile_buf[compile_idx++] = (Cell){.word = zbranch};
+    compile_buf[compile_idx++] = (Cell){.word = w_zbranch};
     // compile_push current index (where the offset will be placed)
     compile_push(compile_idx);
     compile_idx++;   // reserve offset cell
@@ -645,7 +643,7 @@ void do_if(Word* w) {
 
 void do_then(Word* w) {
     (void)w;
-    if (state != 1) { printf("THEN only valid in compile mode\n"); return; }
+    if (state != 1) { fprintf(stderr, "THEN only valid in compile mode\n"); return; }
     int64_t offset_idx = compile_pop();
     if (offset_idx < 0) return;
     compile_buf[offset_idx].num = compile_idx - offset_idx;
@@ -653,52 +651,49 @@ void do_then(Word* w) {
 
 void do_else(Word* w) {
     (void)w;
-    if (state != 1) { printf("ELSE only valid in compile mode\n"); return; }
+    if (state != 1) { fprintf(stderr, "ELSE only valid in compile mode\n"); return; }
     int64_t if_offset_idx = compile_pop();
     if (if_offset_idx < 0) return;
 
-    Word* branch_w = lookup_word_internal("branch");
-    if (!branch_w) { printf("Fatal: branch not found\n"); return; }
+    if (!w_branch) { fprintf(stderr, "Fatal: branch not found\n"); return; }
     ensure_compile_cap(2);
 
     // resolve IF offset to skip the ELSE branch
     compile_buf[if_offset_idx].num = (compile_idx + 2) - if_offset_idx;
 
     // compile unconditional branch for ELSE part
-    compile_buf[compile_idx++] = (Cell){.word = branch_w};
+    compile_buf[compile_idx++] = (Cell){.word = w_branch};
     compile_push(compile_idx);
     compile_idx++;   // reserve offset cell
 }
 
 void do_begin(Word* w) {
     (void)w;
-    if (state != 1) { printf("BEGIN only valid in compile mode\n"); return; }
+    if (state != 1) { fprintf(stderr, "BEGIN only valid in compile mode\n"); return; }
     compile_push(compile_idx);
 }
 
 void do_until(Word* w) {
     (void)w;
-    if (state != 1) { printf("UNTIL only valid in compile mode\n"); return; }
+    if (state != 1) { fprintf(stderr, "UNTIL only valid in compile mode\n"); return; }
     int64_t begin_idx = compile_pop();
     if (begin_idx < 0) return;
 
-    Word* zbranch = lookup_word_internal("0branch");
-    if (!zbranch) { printf("Fatal: 0branch not found\n"); return; }
+    if (!w_zbranch) { fprintf(stderr, "Fatal: 0branch not found\n"); return; }
     ensure_compile_cap(2);
-    compile_buf[compile_idx++] = (Cell){.word = zbranch};
+    compile_buf[compile_idx++] = (Cell){.word = w_zbranch};
     compile_buf[compile_idx++] = (Cell){.num = begin_idx - compile_idx};
 }
 
 void do_while(Word* w) {
     (void)w;
-    if (state != 1) { printf("WHILE only valid in compile mode\n"); return; }
+    if (state != 1) { fprintf(stderr, "WHILE only valid in compile mode\n"); return; }
     int64_t begin_idx = compile_pop();
     if (begin_idx < 0) return;
 
-    Word* zbranch = lookup_word_internal("0branch");
-    if (!zbranch) { printf("Fatal: 0branch not found\n"); return; }
+    if (!w_zbranch) { fprintf(stderr, "Fatal: 0branch not found\n"); return; }
     ensure_compile_cap(2);
-    compile_buf[compile_idx++] = (Cell){.word = zbranch};
+    compile_buf[compile_idx++] = (Cell){.word = w_zbranch};
     int64_t while_offset_idx = compile_idx;
     compile_idx++;   // reserve offset
 
@@ -708,16 +703,15 @@ void do_while(Word* w) {
 
 void do_repeat(Word* w) {
     (void)w;
-    if (state != 1) { printf("REPEAT only valid in compile mode\n"); return; }
+    if (state != 1) { fprintf(stderr, "REPEAT only valid in compile mode\n"); return; }
     int64_t begin_idx = compile_pop();
     if (begin_idx < 0) return;
     int64_t while_offset_idx = compile_pop();
     if (while_offset_idx < 0) return;
 
-    Word* branch_w = lookup_word_internal("branch");
-    if (!branch_w) { printf("Fatal: branch not found\n"); return; }
+    if (!w_branch) { fprintf(stderr, "Fatal: branch not found\n"); return; }
     ensure_compile_cap(2);
-    compile_buf[compile_idx++] = (Cell){.word = branch_w};
+    compile_buf[compile_idx++] = (Cell){.word = w_branch};
     compile_buf[compile_idx++] = (Cell){.num = begin_idx - compile_idx};
 
     compile_buf[while_offset_idx].num = compile_idx - while_offset_idx;
@@ -755,10 +749,9 @@ void do_roll(Word* w) {
 void do_qdup(Word* w) {
     (void)w;
     if (data_sp < 0) return;
-    int64_t v = data_pop();
+    int64_t v = data_stack[data_sp];
     if (v != 0) {
         data_push(v);
-        data_push(v);
     }
 }
 
@@ -780,12 +773,12 @@ void do_2drop(Word* w) {
 void do_2swap(Word* w) {
     (void)w;
     if (data_sp < 3) return;
-    int64_t d = data_pop(); // x4
-    int64_t c = data_pop(); // x3
-    int64_t b = data_pop(); // x2
-    int64_t a = data_pop(); // x1
-    data_push(b);
-    data_push(a);
-    data_push(d);
-    data_push(c);
+    int64_t x4 = data_pop();
+    int64_t x3 = data_pop();
+    int64_t x2 = data_pop();
+    int64_t x1 = data_pop();
+    data_push(x3);
+    data_push(x4);
+    data_push(x1);
+    data_push(x2);
 }
diff --git a/main.c b/main.c
index 3447169..13cfae6 100644
--- a/main.c
+++ b/main.c
@@ -11,12 +11,12 @@ int main(void) {
     here = user_mem;
 
     // Hidden words first
-    add_primitive("exit",    do_exit,    0);
-    add_primitive("docolon", do_docolon, 1 << 6);
-    add_primitive("lit",     do_lit,     1 << 6);
-    add_primitive("do_dot_quote_inner", do_dot_quote_inner, 1 << 6);
-    add_primitive("0branch", do_zero_branch, 1 << 6);
-    add_primitive("branch",  do_branch,  1 << 6);
+    w_exit = add_primitive("exit",    do_exit,    0);
+    w_docolon = add_primitive("docolon", do_docolon, F_HIDDEN);
+    w_lit = add_primitive("lit",     do_lit,     F_HIDDEN);
+    w_dot_quote_inner = add_primitive("do_dot_quote_inner", do_dot_quote_inner, F_HIDDEN);
+    w_zbranch = add_primitive("0branch", do_zero_branch, F_HIDDEN);
+    w_branch = add_primitive("branch",  do_branch,  F_HIDDEN);
 
     // Public primitives
     // Stack ops
@@ -69,7 +69,7 @@ int main(void) {
     add_primitive("cr",    do_cr, 0);
     add_primitive("emit",  do_emit, 0);
     add_primitive("key",   do_key, 0);
-    add_primitive(".\"",   do_dot_quote, 1 << 7); // immediate
+    add_primitive(".\"",   do_dot_quote, F_IMMEDIATE); // immediate
     add_primitive("words", do_words, 0);
 
     // Memory
@@ -90,14 +90,14 @@ int main(void) {
 
     // Compilation / control flow
     add_primitive(":",     do_colon, 0);
-    add_primitive(";",     do_semicolon, 1 << 7);
-    add_primitive("if",    do_if, 1 << 7);
-    add_primitive("else",  do_else, 1 << 7);
-    add_primitive("then",  do_then, 1 << 7);
-    add_primitive("begin", do_begin, 1 << 7);
-    add_primitive("until", do_until, 1 << 7);
-    add_primitive("while", do_while, 1 << 7);
-    add_primitive("repeat", do_repeat, 1 << 7);
+    add_primitive(";",     do_semicolon, F_IMMEDIATE);
+    add_primitive("if",    do_if, F_IMMEDIATE);
+    add_primitive("else",  do_else, F_IMMEDIATE);
+    add_primitive("then",  do_then, F_IMMEDIATE);
+    add_primitive("begin", do_begin, F_IMMEDIATE);
+    add_primitive("until", do_until, F_IMMEDIATE);
+    add_primitive("while", do_while, F_IMMEDIATE);
+    add_primitive("repeat", do_repeat, F_IMMEDIATE);
 
     /* Additional words */
     add_primitive("depth", do_depth, 0);