运行出错误

<?php 

echo $m1 = memory_get_usage(); 

echo "<br />";

$var_string = "123"; 

echo $m2 = memory_get_usage()-$m1; 

echo "<br />";

$n = 123; 

echo $m3 = memory_get_usage()-$m1-$m2; 

echo "<br />";

$f = 123.00; 

echo $m4 = memory_get_usage()-$m1-$m2-$m3; 

echo "<br />";

$var_array("123"); 

echo $m5 = memory_get_usage()-$m1-$m2-$m3-$m4; 

?>