Question

echo "1" . (print '2') + 3; returns 214. How does the script end up with *14?

Answer 1

When you do

echo "1" . (print '2') + 3;

PHP will do (demo)

line     # *  op                           fetch          ext  return  operands
---------------------------------------------------------------------------------
   2     0  >   PRINT                                            ~0      '2'
         1      CONCAT                                           ~1      '1', ~0
         2      ADD                                              ~2      ~1, 3
         3      ECHO                                                     ~2
         4    > RETURN                                                   1

In words:

• print 2, return 1
• concat “1” with returned 1 => “11”
• add “11” + 3 => 14
• echo 14

and that’s 214.

The operators + - . have equal Operator Precedence, but are left associative:

For operators of equal precedence, left associativity means that evaluation proceeds from left to right, and right associativity means the opposite.

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Edit: since all the other answers claim PHP does 1+3, here is further proof that it doesnt:

echo "1" . (print '2') + 9;

gives 220, e.g. 11+9 and not 1 . (1+9). If the addition had precedence over the concatenation, it would have been 2110, but for that you’d had to write

echo "1" . ((print '2') + 9);