diff --git a/src/collections/Array.h b/src/collections/Array.h
index 24a4255..93394c3 100644
--- a/src/collections/Array.h
+++ b/src/collections/Array.h
@@ -12,9 +12,9 @@
     }\
     \
     static inline Array_##T Array_##T##_alloc(u32 len){\
-        return Array_##T##_construct(malloc(len * sizeof(T)), len);\
+        return Array_##T##_construct((T*)malloc(len * sizeof(T)), len);\
     }\
     static inline void Array_##T##_realloc(Array_##T* ptr, u32 new_len){\
-        ptr->data = realloc(ptr->data, new_len * sizeof(T));\
+        ptr->data = (T*)realloc(ptr->data, new_len * sizeof(T));\
         ptr->len = new_len;\
     }
diff --git a/src/collections/List.h b/src/collections/List.h
index 5dc523a..b72cb8d 100644
--- a/src/collections/List.h
+++ b/src/collections/List.h
@@ -1,6 +1,9 @@
 #pragma once
 #include "../std.h"
 
+// minimal max_len after initial (0)
+#define __List_min_size 16
+
 #define List_declare(T)\
     typedef struct List_##T {\
         T* data;\
@@ -14,35 +17,42 @@
     \
     List_##T List_##T##_alloc(u32 initial_len);\
     \
-    T* List_##T##_expand(List_##T* ptr);\
+    T* List_##T##_expand(List_##T* ptr, u32 count);\
     void List_##T##_push(List_##T* ptr, T value);\
+    void List_##T##_pushMany(List_##T* ptr, T* values, u32 count);\
 
 
 #define List_define(T)\
     List_##T List_##T##_alloc(u32 initial_len){\
         if(initial_len == 0)\
             return List_##T##_construct((T*)NULL, 0, 0);\
-        u32 max_Len = ALIGN_TO(initial_len, sizeof(void*)/sizeof(T));\
+        u32 max_len = ALIGN_TO(initial_len, sizeof(void*)/sizeof(T));\
         /* branchless version of max(max_len, __List_min_size) */\
         max_len += (max_len < __List_min_size) * (__List_min_size - max_len);\
         return List_##T##_construct((T*)malloc(initial_len * sizeof(T)), 0, max_len);\
     }\
     \
-    T* List_##T##_expand(List_##T* ptr){\
-        if(ptr->len == ptr->max_len){\
-            ptr->max_len *= 2;\
-            ptr->data = (T*)realloc(ptr->data, ptr->max_len * sizeof(T));\
-            ptr->max_len = max_len;\
+    T* List_##T##_expand(List_##T* ptr, u32 count){\
+        u32 occupied_len = ptr->len;\
+        u32 expanded_max_len = ptr->max_len;\
+        ptr->len += count;\
+        while(ptr->len > ptr->max_len){\
+            expanded_max_len *= 2;\
         }\
-        return &ptr->data[ptr->len++];\
+        ptr->data = (T*)realloc(ptr->data, expanded_max_len * sizeof(T));\
+        return ptr->data + occupied_len;\
     }\
     \
     void List_##T##_push(List_##T* ptr, T value){\
-        T* empty_cell_ptr = List_##T##_expand(ptr);\
+        T* empty_cell_ptr = List_##T##_expand(ptr, 1);\
         *empty_cell_ptr = value;\
     }\
+    \
+    void List_##T##_pushMany(List_##T* ptr, T* values, u32 count){\
+        T* empty_cell_ptr = List_##T##_expand(ptr, count);\
+        memcpy(empty_cell_ptr, values, count * sizeof(T));\
+    }\
 
-#define __List_min_size 16
 
 List_declare(cstr);
 List_declare(u32);
diff --git a/src/compiler/AST.c b/src/compiler/AST.c
index 76c1b1e..f5d4625 100644
--- a/src/compiler/AST.c
+++ b/src/compiler/AST.c
@@ -3,6 +3,7 @@
 List_define(Argument);
 List_define(Operation);
 List_define(DataDefinition);
+List_define(Section);
 
 static cstr _ArgumentType_str[] = {
     "Unset",
diff --git a/src/compiler/Parser.c b/src/compiler/Parser.c
index c0b591b..7af60a2 100644
--- a/src/compiler/Parser.c
+++ b/src/compiler/Parser.c
@@ -85,7 +85,7 @@ static void parseDataDefinition(Compiler* cmp, char* instr_name, DataDefinition*
     Token tok = cmp->tokens.data[++cmp->tok_i];
     char* tok_str = Compiler_extractTokenStr(cmp, tok);
     u8* processed_str = NULL;
-    i32 len = 0;
+    u32 len = 0;
     ddf->name = tok_str;
     
     while(++cmp->tok_i < cmp->tokens.len){
@@ -114,7 +114,7 @@ static void parseDataDefinition(Compiler* cmp, char* instr_name, DataDefinition*
                 tok_str = Compiler_extractTokenStr(cmp, tok);
                 processed_str = resolveEscapeSequences(cmp, tok_str);
                 free(tok_str);
-                len = strlen(processed_str);
+                len = strlen((char*)processed_str);
                 if(len != ddf->element_size){
                     setError("can't fit char of size %i in %u bit variable", len, _element_size_bits);
                     return;
@@ -127,7 +127,7 @@ static void parseDataDefinition(Compiler* cmp, char* instr_name, DataDefinition*
                 tok_str = Compiler_extractTokenStr(cmp, tok);
                 processed_str = resolveEscapeSequences(cmp, tok_str);
                 free(tok_str);
-                len = strlen(processed_str);
+                len = strlen((char*)processed_str);
                 List_u8_pushBytes(&ddf->data, processed_str, 0, len);
                 break;
             case TokenType_OperationEnd:
@@ -161,7 +161,7 @@ bool Compiler_parse(Compiler* cmp){
                 break;
             case TokenType_Label:
                 // create new section
-                sec = List_Section_expand(&cmp->ast.sections);
+                sec = List_Section_expand(&cmp->ast.sections, 1);
                 Section_init(sec, Compiler_extractTokenStr(cmp, tok));
                 break;
             case TokenType_Instruction:
@@ -170,11 +170,11 @@ bool Compiler_parse(Compiler* cmp){
                 char* instr_name = Compiler_extractTokenStr(cmp, tok);
                 // data definition starts with const
                 if(cstr_seek(instr_name, "const", 0, 1)){
-                    DataDefinition* dataDefPtr = List_DataDefinition_expand(&sec->data);
+                    DataDefinition* dataDefPtr = List_DataDefinition_expand(&sec->data, 1);
                     parseDataDefinition(cmp, instr_name, dataDefPtr);
                 }
                 else {
-                    Operation* operPtr = List_Operation_expand(&sec->code);
+                    Operation* operPtr = List_Operation_expand(&sec->code, 1);
                     parseOperation(cmp, instr_name, operPtr);
                 }
                 break;
diff --git a/src/string/StringBuilder.c b/src/string/StringBuilder.c
new file mode 100644
index 0000000..8db4361
--- /dev/null
+++ b/src/string/StringBuilder.c
@@ -0,0 +1,43 @@
+#include "StringBuilder.h"
+
+void StringBuilder_free(StringBuilder* b){
+    free(b->buffer.data);
+}
+
+str StringBuilder_build(StringBuilder* b){
+    List_u8_push(&b->buffer, '\0');
+    str result = str_construct((char*)b->buffer.data, b->buffer.len - 1, true);
+    return result;
+}
+
+
+void StringBuilder_append_char(StringBuilder* b, char c){
+    List_u8_push(&b->buffer, c);
+}
+
+
+void StringBuilder_append_string(StringBuilder* b, str s){
+    List_u8_pushMany(&b->buffer, (u8*)s.data, s.len);
+}
+
+void StringBuilder_append_cstr(StringBuilder* b, char* s){
+    StringBuilder_append_string(b, str_construct(s, strlen(s), true));
+}
+
+void StringBuilder_append_i64(StringBuilder* b, i64 n){
+    char buf[32];
+    sprintf_s(buf, sizeof(buf), "%llu", n);
+    StringBuilder_append_cstr(b, buf);
+}
+
+void StringBuilder_append_u64(StringBuilder* b, u64 n){
+    char buf[32];
+    sprintf_s(buf, sizeof(buf), "%llu", n);
+    StringBuilder_append_cstr(b, buf);
+}
+
+void StringBuilder_append_f64(StringBuilder* b, f64 n){
+    char buf[32];
+    sprintf_s(buf, sizeof(buf), "%lf", n);
+    StringBuilder_append_cstr(b, buf);
+}
diff --git a/src/string/StringBuilder.h b/src/string/StringBuilder.h
new file mode 100644
index 0000000..3d5d766
--- /dev/null
+++ b/src/string/StringBuilder.h
@@ -0,0 +1,32 @@
+#pragma once
+
+#if __cplusplus
+extern "C" {
+#endif
+
+#include "../collections/List.h"
+#include "str.h"
+
+typedef struct StringBuilder {
+	List_u8 buffer;
+} StringBuilder;
+
+static inline StringBuilder StringBuilder_construct(u32 initial_size) { 
+    return (StringBuilder){ .buffer = List_u8_alloc(initial_size) }; 
+}
+void StringBuilder_free(StringBuilder* b);
+
+void StringBuilder_removeFromEnd(StringBuilder* b, u32 count);
+void StringBuilder_append_char(StringBuilder* b, char c);
+void StringBuilder_append_cstr(StringBuilder* b, char* s);
+void StringBuilder_append_string(StringBuilder* b, str s);
+void StringBuilder_append_i64(StringBuilder* b, i64 a);
+void StringBuilder_append_u64(StringBuilder* b, u64 a);
+void StringBuilder_append_f64(StringBuilder* b, f64 a);
+
+// adds '\0' to the buffer and returns pointer to buffer content
+str StringBuilder_getStr(StringBuilder* b);
+
+#if __cplusplus
+}
+#endif
\ No newline at end of file
diff --git a/src/string/str.c b/src/string/str.c
new file mode 100644
index 0000000..52af538
--- /dev/null
+++ b/src/string/str.c
@@ -0,0 +1,29 @@
+#include "str.h"
+
+str str_copy(str src){
+    if(src.data == NULL || src.len == 0)
+        return src;
+    str nstr = str_construct((char*)malloc(src.len + 1), src.len, true);
+    memcpy(nstr.data, src.data, src.len);
+    nstr.data[nstr.len] = '\0';
+    return nstr;
+}
+
+bool str_compare(str str0, str str1){
+    if(str0.len!= str1.len) return false;
+    if(!str0.data) return str1.data ? false : true;
+    else if(!str1.data) return false;
+    while(str0.len-- > 0)
+        if(*str0.data++ != *str1.data++ ) 
+            return false;
+    return true;
+}
+
+str str_reverse(str s){
+    if(s.data == NULL || s.len == 0)
+        return s;
+    str r = str_construct(malloc(s.len), s.len, s.isZeroTerminated);
+    for(u32 i = 0; i < s.len; i++ )
+        r.data[i] = s.data[s.len - i - 1];
+    return r;
+}
diff --git a/src/string/str.h b/src/string/str.h
new file mode 100644
index 0000000..c53585a
--- /dev/null
+++ b/src/string/str.h
@@ -0,0 +1,30 @@
+#pragma once
+
+#include "../std.h"
+
+typedef struct str {
+    char* data;
+    u32 len;
+    bool isZeroTerminated;
+} str;
+
+#define str_construct(DATA, LEN, ZERO_TERMINATED) ((str){ .data = DATA, .len = LEN, .isZeroTerminated = ZERO_TERMINATED })
+
+static const str str_null = str_construct(NULL, 0, 0);
+
+
+/// copies str content to new char pointer value (adding '\0' at the end)
+char* str_extractcstr(str str);
+
+/// copies src content to new string and adds \0 at the end
+str str_copy(str src);
+
+/// compares two strings, NullPtr-friendly
+bool str_compare(str str0, str str1);
+
+/// allocates new string which is reversed variant of <s>
+str str_reverse(str s);
+
+#if __cplusplus
+}
+#endif
\ No newline at end of file