第五行没错啊
<?php
$num_float1 = 1.234;
echo $num_float1;
echo "<br />";
$unm_float2 = 1.2e3;
echo $num_float2;
echo "<br />";
$unm_float3 = 1.2e-1;
echo $num_float3;
echo "<br />";
?>
定义的变量和输出的不是一个东西
是$num_float2而不是$unm_float2;
<?php
$num_float1 = 1.234;
echo $num_float1;
echo "<br />";
$num_float2 = 1.2e3;
echo $num_float2;
echo "<br />";
$unm_float3 = 7.0E-1;
echo $num_float3;
echo "<br />";
?>
你把变量名写成$unm_float2,$unm_float3了
变量名是$num_float2,$num_float3