Arithmetic operation within string concatenation without parenthesis causes strange result

Question

Consider the following line of code:

The output of that is 3, which is the expec

Answer 1

In this code:

echo '10 - 7 = '.$x-$y;

The concatenation takes precedence, so what you're left with is this:

echo '10 - 7 = 10'-$y;

Because this is trying to perform integer subtraction with a string, the string is converted to an integer first, so you're left with something like this:

echo (int)'10 - 7 = 10'-$y;

The integer value of that string is 10, so the resulting arithmetic looks like this:

echo 10-$y;

Because $y is 7, and 10 - 7 = 3, the result being echoed is 3.