Comparison between a numeric and an alphanumeric string

1e0 is the scientific notation for 1 i.e 1 vezes 10 elevado a 0. E php converts numeric strings in numbers to make the comparison.

var_dump("1000" == "1e3"); //1000 == 1000 -> true 
var_dump("1" == "1e0"); //1 == 1 -> true 

1e0e is not a

var_dump("1" == "1e0e"); //1 != da string "1e0e"

Whenever you do the casting you will see that this occurs because casting forces the conversion to integer:

var_dump((int)"1" == (int)"1e0e"); // true

To avoid confusion at the time of the comparison use === instead of == , so in addition to content PHP will compare type too.

var_dump("1" === "1e0"); // false

String "1" is different from string "1e0"

var_dump("1" === "1e0e"); // false

String "1" is different from string "1e0e"

var_dump((int)"1" == (int)"1e0e"); // true

Integer 1 is equal to integer 1

Compare === does not resolve, see 0xFA is 250, so (250 === 0xFA) results in TRUE

1) Compare the length of a string for an input that is: 0xFA

if( $string <= 255 ) // 250 < 255 // Logo retornará TRUE

2) Convert to string causes the same effect:

( (string)255 === (string)0xFF )

Your example:

Here you have a simple string comparison, 1e0e does not assume integer value and 1 == 1 is not the operation that occurs.

var_dump("1" == "1e0e"); //1 == 1 -> false???

Here you have 1e0e as a string and when it converts to INT, it naturally assumes the value of 1, which added to 1 results in 2;

echo (int)"1" + (int)"1e0e"; // 2

If you want to compare effectively, you will need to do a combination of checks:
. You can force the input to assume a string value with (string)$input
. Combine mb_strlen to compare the length of the entries.

If you can, more information about the type of verification.