0 Compares (operator ==) with any leading string that is not a number (or, in other words, a character that cannot be converted to a number), and returns true.
The reason is that when comparing numbers with strings, first try to convert the string into a number, and then compare. If a string cannot be converted into a number, the conversion result is 0, so comparing with 0 always returns true.
More detailed comparison rules, multiple types of comparison rules, can be found in PHP Manual/Language Reference/Operators/Comparison Operators.
Be used as two in PHP When comparing numeric strings (strings containing only numbers), they are directly converted into numerical values for comparison
The following example: (note that the last digits of the two variables $a and $b are not equal)
Copy code The code is as follows:
//Example 1
$a = '511203199106034578';
$b = '511203199106034579';
if ($a==$b) {
echo 'equal';
} else {
echo 'notEqual';
}
?>
Run the above program but found that the result is equal (not the result we thought)
We add a letter a to $a and $b respectively
Copy code The code is as follows:
//Example 2
$a = 'a511203199106034578';
$b = 'a511203199106034579';
if ($a==$b) {
echo 'equal';
} else {
echo 'notEqual';
}
?>
This time the output is notEqual (the correct result)
Example 1 is equal because PHP combines two numeric strings Convert to numeric type, and the two numbers are exactly equal to the following example
Copy the code The code is as follows:
$a = 511203199106034578;
$b = 511203199106034579;
echo $a; // Output 5.1120319910603E+17 which is 511203199106030000
echo $b; // Output 5.1120319910603E+17 which is 511203199106030000
?>
So the result we got in example 1 is equal
To avoid this unexpected result is to use the type comparison operator === as in the following example ( If $a is equal to $b, and their types are also the same)
Copy code The code is as follows:
//Example 4
$a = '511203199106034578';
$b = '511203199106034579';
if ($a===$b) {
echo 'equal';
} else {
echo 'notEqual';
}
?>
This way we can get the expected notEqual
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