adding extern msgbox example

Author: Whitecat18

Exec_Extern/MessageBox.rs

@@ -0,0 +1,22 @@
+// Just an sample Example of using using extern to Run MessageBoxA ..!
+// Create an Function with the help of Microsoft Documentation !
+
+use std::ptr::null_mut;
+
+extern "system" {
+    fn MessageBoxA(
+        hWnd: *mut std::ffi::c_void,
+        lpText: *const u8,
+        lpCaption: *const u8,
+        uType: u32,
+    ) -> i32;
+}
+
+fn main() {
+    let text = b"Hello Nerds..\0".as_ptr();
+    let caption = b"Meow_Meow\0".as_ptr();
+
+    unsafe {
+        MessageBoxA(null_mut(), text, caption, 0x00000000);
+    }
+}

Exec_Extern/README.md

@@ -1 +1,3 @@
-## Execute winapi functions without using windows or winapi crates by calling the functins from the External Library ie original lib that was written in C/C++.
+### Execute winapi functions without using windows or winapi crates by calling the functins from the External Library ie original lib that was written in C/C++.
+
+