Adding string with number in php

It casts '3dollars' as a number, getting $a = 3.

When you echo, you add 20, to $a, so it prints 23 and $a = 23.

Then, when you print, you again add 20, so now $a = 43.

The right way to add (which is technically concatenating) strings is

$a = 7;
$b = "3 dollars";
print ($a . $b);  // 73 dollars

The + operator in php automatically converts string into numbers, which explains why your code carried out arimethic instead of concatenation

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