Execute function after connect to database

Solution 1:

You need to declare variables "global" :

<?php
    $conn = null; // ◄■■■
    $result = null; // ◄■■■

    function connect_to_database($servername, $username,$password,$dbname)
    { global $conn; // ◄■■■
        $conn = new mysqli($servername, $username, $password, $dbname);
        if ($conn->connect_error)
        {
            die("Connection failed: " . $conn->connect_error);
        }
    }

    function execute($get_sql)
    { global $conn; // ◄■■■
      global $result; // ◄■■■
        $sql[0] = $get_sql;
        $result = mysqli_query($conn,$sql[0]); // ◄■■■ $CONN AND $RESULT.
    }

    connect_to_database("localhost","root","root","m1_14");
     execute("INSERT INTO teszt_1 (email,username,order,createdate) " .
             "VALUES ('[email protected]','test','test',NOW())");

    execute("select * from teszt_1");

    foreach ( $result as $row ) // ◄■■■ USE $RESULT HERE.
      echo $row["email"];

Global variables let you pass values from one function to another.

In case of a "insert" you don't need $result, in case of a "select" you can use $result to access the values.