Any programmer in almost any language who mixes types like that without understanding the implicit type conversion semantics is asking for trouble.

Implicit type conversion is evil, and I don't see how PHP's sin of favouring string -> number over number -> string is any worse than, say:

    // Javascript
    console.log(+(+!![]+(+[]+[]))); // outputs the number 10

Or:

    // C, Java

    float celsius, fahrenheit1, fahrenheit2;
    celsius = 100;

    fahrenheit1 = celsius * 9 / 5 + 32;
    fahrenheit2 = 9 / 5 * celsius + 32;

    assert(fahrenheit1 == 212); // OK
    assert(fahrenheit2 == 212); // Oops!  It's 132.  What happened?