Why Does PHP Echo \"2\" When Adding and Concatenating Integers?

PHP's Intriguing Behavior: Unraveling the Sum and Concatenation Quandary

In the realm of PHP programming, the recent discussion regarding the perplexing behavior when adding and concatenating values has sparked curiosity.

Let us delve into this anomaly, as demonstrated by the following code snippet:

<code class="php">$a = 1;
$b = 2;

echo "sum: " .  $a + $b;
echo "sum: " . ($a + $b);</code>

Upon executing this code, one would expect both echoes to output "sum: 3". However, surprisingly, the first echo displays "2," leaving developers baffled. Why does this happen?

The key lies in the operator precedence and associativity in PHP. Both the addition ( ) and concatenation (.) operators share the same precedence level, making them left associative. The order in which these operators are evaluated becomes crucial:

1. In the first echo, the concatenation is performed first, resulting in "sum: 1".
2. This string is then converted to an integer due to the numeric context, effectively converting the addition to 0 2, yielding "2."

However, in the second echo, the parentheses ensure that the addition occurs before the concatenation, giving us the desired result, "sum: 3."

This intriguing behavior, though not explicitly documented, can be discovered through experimentation and understanding the subtle nuances of operator precedence and associativity in PHP.

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