Question

Let’s say I have file foo.txt in which I have one digit which is 0.
Then I read that file and 0 is stored into array. I want to increment number by 1 so I just use shorthand operator ++ but it doesn’t work however += does.

$poo = file("foo.txt");
$poo[0]++;
echo $poo; // gives me 0
$poo[0] += 1;
echo $poo; // gives me 1

I know that when I read file value of poo[0] is string with space "0 " but why it doesn’t work with ++?

Answer 1

You have encountered a common error in languages that use implicit type casting. When you read the contents of foo.txt into $poo, the value is stored as a string.

When you tell PHP to increment the string using ++, PHP has to try to determine what you mean. $poo contains a string (not a number) so PHP doesn’t know that you want to add the value of 0 + 1; instead, it thinks you are trying to perform a string operation and provides an unexpected result.

In the second case, the implicit typing figures out that, since you use an integer (not a string) on the right side of the equation, you must want to cast the left side to an integer as well.

To be safe, you should explicitly tell the PHP interpreter that you are trying to perform a mathematical operation on two numbers:

$poo[0] = (int)$poo[0] + 1;

For more information please see PHP: Type Juggling.