如何在php中添加来自不同函数的两个独立变量？

function function1() {
    global $var1;
    $var1 = 10;
}

function function2() {
    global $var1;
    $var2 = 20;
    $result = $var1 + $var2;
    echo $result;
}

function1();
function2();  // 输出：30

function function1() {
    $var1 = 10;
    return $var1;
}

function function2() {
    $var2 = 20;
    return $var2;
}

$var1 = function1();
$var2 = function2();
$result = $var1 + $var2;
echo $result;  // 输出：30

function function1($var1) {
    $var1 += 10;
    return $var1;
}

function function2($var2) {
    $var2 += 20;
    return $var2;
}

$var1 = 10;
$var2 = 20;
$var1 = function1($var1);
$var2 = function2($var2);
$result = $var1 + $var2;
echo $result;  // 输出：60