edecode

Hello guys, I am studying about function eval() and I can't know how and why this functions is necessary! I wrote this code: <?php $string = "beautiful"; $time = "winter"; $str = 'This is a $string $time morning!'; echo $str. "<br>"; eval("\$str = \"$str\";"); echo $str; $code1 = "echo 'Hello World!'; "; $code2 = "?>"; $code_php = '<?php $code1 $code2'; echo $code_php; eval("\$code_php = \"$code_php\";"); echo $code_php; ?> On first echo the result should be this: "This is a beautiful winter morning!", that's right? On second echo the result should be a code in php "This is a $string $time morning!" On third echo the result should be this: "Hello World" Lastly, the fourth echo the result should be a code in php: "<?php $code1 $code2" Am I do this right? Thanks