diff --git a/headers/stdlib.h b/headers/stdlib.h
new file mode 100644
index 0000000..3510f6d
--- /dev/null
+++ b/headers/stdlib.h
@@ -0,0 +1,5 @@
+#pragma once
+
+int atoi(const char *nptr);
+long atol(const char *nptr);
+long long atoll(const char *nptr);
\ No newline at end of file
diff --git a/src/stdlib/atoi.c b/src/stdlib/atoi.c
new file mode 100644
index 0000000..7d8595f
--- /dev/null
+++ b/src/stdlib/atoi.c
@@ -0,0 +1,6 @@
+#include "../../headers/stdlib.h"
+
+int atoi(const char *str)
+{
+    return atoll(str);
+}
\ No newline at end of file
diff --git a/src/stdlib/atol.c b/src/stdlib/atol.c
new file mode 100644
index 0000000..2ce9be3
--- /dev/null
+++ b/src/stdlib/atol.c
@@ -0,0 +1,6 @@
+#include "../../headers/stdlib.h"
+
+long atol(const char *str)
+{
+    return atoll(str);
+}
\ No newline at end of file
diff --git a/src/stdlib/atoll.c b/src/stdlib/atoll.c
new file mode 100644
index 0000000..4a72c5e
--- /dev/null
+++ b/src/stdlib/atoll.c
@@ -0,0 +1,13 @@
+#include "../../headers/ctype.h"
+
+long long atoll(const char *str)
+{
+    const char *start = str;
+    long long ret;
+
+    while (*start != '\0') {
+        if (isdigit(*str))
+            ret = ret * 10 + *str - '0';
+    }
+    return ret;
+}
\ No newline at end of file