<?php

$servername = "localhost";
$username = "curso";
$password = "1234";

// Create connection
$conn = mysqli_connect($servername, $username, $password);

// Check connection
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}
echo "Conexion Exitosa";

$bd_seleccionada = mysql_select_db($conn,"basededatos"); // Linea 19 del error
if (!$bd_seleccionada) {
     die("Conecion fallida: " . mysqli_error());
}
echo "Conexion Exitosa";
?>