The values appearing in the PHP operation code feel confused, please help explain.

Header ("Content-type:text/html;charset=utf-8");
$a = 10;
$b = ' 60 ';
echo "$a + $b =". $a + $b. "
";
echo "$a-$b =". $a-$b. "
";
echo "$a $b = ". $a$b. "
";
echo "$a/$b =". $a/$b. "
";
?>

The last page output has the following values:
70
-50
10*60=600
10/60=0.16666666666667

How are these values derived?

Reply content:

Header ("Content-type:text/html;charset=utf-8");
$a = 10;
$b = ' 60 ';
echo "$a + $b =". $a + $b. "
";
echo "$a-$b =". $a-$b. "
";
echo "$a$b =". $a$b. "
";
echo "$a/$b =". $a/$b. "
";
?>

The last page output has the following values:
70
-50
10*60=600
10/60=0.16666666666667

How are these values derived?

echo "$a + $b =". $a + $b. "
"; execution result (+-) is the same level of execution order left to right)

"$a+$b=" => '10+60='"$a+$b=".$a => '10+60=10'("$a+$b=".$a) + $b => intval('10+60=10') + intval($b) => 10+60 =>70

Click to view PHP operator precedence

$a is the integer type, stored in PHP as Long, $b is a string, when doing arithmetic operations to cast to an integer, the division of the decimal number is stored in double, the rest is mathematical transport forget

Basic operation: Subtraction

In this case, the string is automatically converted into an shaping engagement operation

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