diff --git a/str.c b/str.c
index 8036bd5..98ebaf0 100644
--- a/str.c
+++ b/str.c
@@ -28,7 +28,10 @@ void
 str_init(str *s)
 {
 	assert(s);
-	// <YOURCODE>
+	s->len = 0;
+	s->capacity = INIT_SZ;
+	s->ptr = xmalloc(INIT_SZ);
+	s->ptr[0] = '\0';
 }
 
 void
@@ -37,64 +40,86 @@ str_deinit(str *s)
 	if (s->ptr)
 		free(s->ptr);
 	s->ptr = NULL;
+	s->len = 0;
+	s->capacity = 0;
 }
 
 void
 str_init_data(str *s, const char *initial)
 {
 	assert(s && initial);
-	// <YOURCODE>
+	int len = strlen(initial);
+	s->len = len;
+	s->capacity = len + 1;
+	s->ptr = xmalloc(s->capacity);
+	memcpy(s->ptr, initial, len + 1);
 }
 
 char *
 str_data(str *s)
 {
 	assert(s);
-	// <YOURCODE>
-	return NULL;
+	return s->ptr;
 }
 
 void
 str_set(str *s, char *cstr)
 {
 	assert(s && cstr);
-	// <YOURCODE>
+	int len = strlen(cstr);
+	_str_ensure(s, len);
+	memcpy(s->ptr, cstr, len + 1);
+	s->len = len;
 }
 
 str
 str_copy(str *s)
 {
 	assert(s);
-	// <YOURCODE>
+	str new_str;
+	str_init_data(&new_str, s->ptr);
+	return new_str;
 }
 
 int
 str_count(str *s, char ch)
 {
 	assert(s);
-	// <YOURCODE>
-	return 0;
+	int count = 0;
+	for (int i = 0; i < s->len; i++) {
+		if (s->ptr[i] == ch) {
+			count++;
+		}
+	}
+	return count;
 }
 
 void
 str_append(str *s, char *cstr)
 {
 	assert(s && cstr);
-	// <YOURCODE>
+	int len = strlen(cstr);
+	str_append_n(s, cstr, len);
 }
 
 void
 str_append_n(str *s, char *cstr, int len)
 {
 	assert(s && cstr);
-	// <YOURCODE>
+	_str_ensure(s, s->len + len);
+	memcpy(s->ptr + s->len, cstr, len);
+	s->len += len;
+	s->ptr[s->len] = '\0';
 }
 
 void
 str_shrink(str *s, int len)
 {
 	assert(s && len >= 0);
-	// <YOURCODE>
+	if (len < s->len) {
+		s->len = len;
+		s->ptr[s->len] = '\0';
+	}
 }
 
 int
@@ -114,7 +139,16 @@ str_sub(str *s, int start_idx, int length)
 
 	str s2;
 	str_init(&s2);
-	// <YOURCODE>
+	if (start_idx >= s->len) {
+		return s2; // пустая строка
+	}
+	
+	int actual_length = length;
+	if (start_idx + length > s->len) {
+		actual_length = s->len - start_idx;
+	}
+	
+	str_append_n(&s2, s->ptr + start_idx, actual_length);
 	return s2;
 }
 
@@ -123,6 +157,29 @@ int
 str_replace(str *s, char *substr, char *replacement)
 {
 	assert(s && substr && replacement);
-	// <YOURCODE>
-	return 0;
+	int substr_len = strlen(substr);
+	int replacement_len = strlen(replacement);
+	int count = 0;
+	
+	str temp;
+	str_init(&temp);
+	
+	int pos = 0;
+	int found_pos;
+	
+	while ((found_pos = str_find(s, substr)) != -1) {
+		str_append_n(&temp, s->ptr + pos, found_pos - pos);
+		str_append(&temp, replacement);
+		pos = found_pos + substr_len;
+		count++;
+	}
+	
+	if (pos < s->len) {
+		str_append_n(&temp, s->ptr + pos, s->len - pos);
+	}
+	
+	str_set(s, str_data(&temp));
+	str_deinit(&temp);
+	
+	return count;
 }
diff --git a/str.h b/str.h
index 8cf04b4..355e22a 100644
--- a/str.h
+++ b/str.h
@@ -60,3 +60,4 @@ str str_sub(str *s, int start_idx, int length);
 //В результате в строке &s должна получиться строка "test bar baz test",
 //функция должна вернуть 2
 int str_replace(str *s, char *substr, char *replacement);
+
diff --git a/str_test b/str_test
new file mode 100755
index 0000000..88f2989
Binary files /dev/null and b/str_test differ