If I have a variable which is given a string that could also be a number, as so:
$a = "1";
If I want to check if it is indeed equal to 1, is there any functional difference between
if((int)$a == 1) {
whatever();
}
and
if($a == "1") {
whatever();
}
Here I am thinking about PHP, but answers about other languages will be welcome.
$a = "1"; // $a is a string
$a = 1; // $a is an integer
1st one
if((int)$a == 1) {
//int == int
whatever();
}
2nd one
if($a == "1") {
//string == string
whatever();
}
But if you do
$a = "1"; // $a is a string
if($a == 1) {
//string & int
//here $a will be automatically cast into int by php
whatever();
}
In the first case you need to convert and then compare while in the second you only compare values. In that sense the second solutions seems better as it avoids unnecessary operations. Also second version is safer as it is possible that $a can not be casted to int.
since your question also asks about other languages you might be looking for more general info, in which case dont forget about triple equals. which is really really equal to something.
$a = "1";
if ($a===1) {
// never gonna happen
}
$b = 1;
if ($b === 1) {
// yep you're a number and you're equal to 1
}
Related
In my never-ending quest to optimise my line usage, I've just got a quick question about what exactly can go into as assignment statement in PHP (and other languages too, but I'm working on a PHP project).
In my program I have a certain boolean variable, which is toggled by a few things summarised by an if statement. I thought, hang on, that if statement will evaluate to a boolean value, can I just use that logic in one line, as opposed to wrapping a separate assignment statement inside the if. Basically my question is will:
$myVar = ($a == $b);
be equivalent to
if ($a == $b) { $myVar = true; }
else { $myVar = false; }
As you can see, this saves me one whole line, so it will impact my project hugely. /sarcasm
What you are looking for is a terinary operation. Something simialar to
$var = ($a === $b ? true : false);
echo $var;
Depending on the evaluation result of $a === $b the value of $var is then set.
Short answer, $myVar = ($a == $b); is the same as if ($a == $b) { $myVar = true; } else { $myVar = false; }.
And if you want to be even shorter, you can even remove the (...) and have it barely $myVar = $a == $b;
If I have a conditional statement
if (A > B || B > C)
Which statement is going to be evaluated first: "A > B" or "B > C"?
Does same order is applied to math statements:
$var = $value1 + $value2 + $value3;
Thanks,
Alex.
In PHP the script is evaluated from left to right unless parenthesis are used, if they are used it evalutes then in logical order. In addition please remember that no code in the if condition block(including evaluators) are ran past the first failing statement. This example will only execute the second echo $a and it's value will be 0
$a = 0;
if(1 == 0 && $a = 5)
{
echo $a;
}
echo $a;
This statement will have $a value of 5 and will execute the statement. Interestingly, the reason that the code will execute is because the $a = 5 assignment in the if sets $a = 5 or " 5 = 5".
if(1 == 1 && $a = 5)
{
echo $a;
}
Also note there are else and else if statements if you have not looked into it
$a =2
if($a == 2)
{
}
else if($a > 2){
echo ">".$a;
}
else{
echo "its none of the conditions";
}
The reason that you use two equals signs is to compare the value type insensitive vs one equal which would be assigning the value. There is also three equals which would compare the type and value example This would evaluate to true :
$a = 2;
if($a == "2")
The following would not be true because you are comparing a String to integer.
$a = 2;
if($a === "2")
Regarding your second questions the same is true of String operators but your syntax is INVALID.
This Example Would say Hellow World:
echo "hellow"."world";
This Example IS NOT DOING CONCATENATION(Though it would do addition if they are integers)
echo "hellow" + "world";
in this simple PHP code
why php parser return true?
$text="51.406ABC917";
$floatval = floatval($text);//51.406
if($floatval==$text){
$result_compare = true;//php parser return true
}else{
$result_compare = false;
}
It's about Type Juggling and PHP type comparison tables, and Comparison Operators. Just check it.
Type of Operand 1:string, resource or number
Type of Operand 2: string, resource or number
Translate strings and resources to numbers, usual math.
You could avoid convertion to float by adding typecasting to string.
if((string)$floatval==$text){
$result_compare = true;
}else{
$result_compare = false; //php parser return false
}
== will compare the data ,use === to compare data and datatype
$floatval==$text
in the above comparison you are comparing a float value with a string
try with === instead of ==
Look here . You should never compare floats for equality.
You need use the epsilon technique.
For example:
if (abs($forstFloat - $secondFloat) < epsilon) {
echo 'they are equal!!'
}
where epsilon is constant representing a very small number.
$a == $b Equal TRUE if $a is equal to $b after type juggling.
$a === $b Identical TRUE if $a is equal to $b, and they are of the same type.
Take this as example
<?php
var_dump(0 == "a"); // 0 == 0 -> true
var_dump("1" == "01"); // 1 == 1 -> true
var_dump("10" == "1e1"); // 10 == 10 -> true
var_dump(100 == "1e2"); // 100 == 100 -> true
switch ("a") {
case 0:
echo "0";
break;
case "a": // never reached because "a" is already matched with 0
echo "a";
break;
}
?>
Reference
Try this,
$text="51.406ABC917";
$floatval = floatval($text);//51.406
if($floatval===$text){
$result_compare = 'true';//php parser return true
}else{
$result_compare = 'failed';
}
LOGIC:
$a == $b Equal TRUE if $a is equal to $b after type juggling.
$a === $b Identical TRUE if $a is equal to $b, and they are of the same type.
Ref: http://www.php.net/manual/en/language.operators.comparison.php
Before comparison $text is converted to a float , with same result as floatval(),
then you compare $floatval==$text, so result is pretty predictable - TRUE
It's normal, when you compare variables from 2 different types, first them to be converted to closest same type.
I would suggest, when comparing float, use similar construct
if ( abs($floatval - floatval($text)) < 0.001 ) {..}
compare difference between 2 floats, instead them. Cause if u have 2 numbers, 45 and 45.00001 , php will think they differ.
What do you wanna accomplish ? Why you think this result is wrong ?
try this:
<?php
$text="51.406ABC917";
$floatval = floatval($text);//51.406
if(strval($floatval)==$text){
$result_compare = true;//php parser return true
}else{
$result_compare = false;
}
?>
If first part of string is numbers, it will be converted to numbers otherwise it will be zero (0). Yes, to compare value and type of variable, use === instead of ==.
But in your case, you already convert string to float by floatval($text); then === same as ==.
The problem is how php convert string to number by floatval($text);
This is how php convert string to numbers:
<?php
$foo = 1 + "10.5"; // $foo is float (11.5)
$foo = 1 + "-1.3e3"; // $foo is float (-1299)
$foo = 1 + "bob-1.3e3"; // $foo is integer (1)
$foo = 1 + "bob3"; // $foo is integer (1)
$foo = 1 + "10 Small Pigs"; // $foo is integer (11)
$foo = 4 + "10.2 Little Piggies"; // $foo is float (14.2)
$foo = "10.0 pigs " + 1; // $foo is float (11)
$foo = "10.0 pigs " + 1.0; // $foo is float (11)
?>
Full document here: http://www.php.net/manual/en/language.types.string.php#language.types.string.conversion
I want to start off by saying that I'm sorry if this question has already been asked- I looked around and there was nothing that matched my query. Basically I want to know how to convert the string "100.0" or "100." to the floats 100.0 and 100.0 and also how to make sure the floats 100.0 and 100. don't equal each other (the same goes for situations like 100. and 100 and 100.0 and 100 Thanks!
Edit: To clarify the not equaling thing here's an example:
Let's say you have a variable $a = 100. and $b = 100.0 I want to make sure $a doesn't equal $b
If you have defined $a and $b like:
$a = 100;
$b = 100.0;
.. then they aren't the same. $a is an integer and $b is a float. You can see this using:
var_dump($a, $b);
But however, as they both are numerice types, you need to compare them using the strict comparison operator ===:
if($a === $b) {
echo "equal";
} else {
echo "not equal";
}
If you have them defined as strings:
$a = "100";
$b = "100.0";
then even the simple equal operator == would work:
if($a == $b) {
echo "equal";
} else {
echo "not equal";
}
PHP:
$a = 2;
$b = 3;
if($b=1 && $a=5)
{
$a++;
$b++;
}
echo $a.'-'.$b;
$a = 2;
$b = 3;
if($a=5 and $b=1)
{
$a++;
$b++;
}
echo $a.'-'.$b;
Output 6-16-2.I don't understand the 1 here.
Perl :
$a = 2;
$b = 3;
if($b=1 && $a=5)
{
$a++;
$b++;
}
print $a.'-'.$b;
$a = 2;
$b = 3;
if($a=5 and $b=1)
{
$a++;
$b++;
}
print $a.'-'.$b;
Output 6-66-2, I don't understand the second 6 here.
Anyone knows the reason?
Actually I know && has higher precedence than and,but I still has the doubt when knowing this before hand.
UPDATE
Now I understand the PHP one,what about the Perl one?
Regarding Perl:
Unlike PHP (but like Python, JavaScript, etc.) the boolean operators don't return a boolean value but the value that made the expression true (or the last value) determines the final result of the expression†(source).
$b=1 && $a=5
is evaluated as
$b = (1 && $a=5) // same as in PHP
which is the same as $b = (1 && 5) (assignment "returns" the assigned value) and assigns 5 to $b.
The bottom line is: The operator precedence is the same in Perl and PHP (at least in this case), but they differ in what value is returned by the boolean operators.
FWIW, PHP's operator precedence can be found here.
What's more interesting (at least this was new to me) is that PHP does not perform type conversion for the increment/decrement operators.
So if $b is true, then $b++ leaves the value as true, while e.g. $b += 1 assigns 2 to $b.
†: What I mean with this is that it returns the first (leftmost) value which
evaluates to false in case of &&
evaluates to true in case of ||
or the last value of the expression.
First example
$a = 2;
$b = 3;
if($b=1 && $a=5) // means $b = (1 && $a=5)
{
var_dump($b); //bool(true) because of &&
$a++;
$b++; //bool(true)++ ==true, ok
}
echo $a.'-'.$b;
hope you will not use those codes in production)
I'm noob in perl but i can suggest a&&b returns a or b (last of them if all of them converted to bool), not boolean, then $b = (1 && $a=5) returns $b=5 (is 5)
here's the issue: 1 && 5 returns 5 in perl. you get the result you expect if you code the conditional as if(($b=1) && ($a=5))
For Perl, fig. 2: and has a very low priority in perl, it's not a synonym of &&'s. Therefore the sample is executed as (($a = 5) and ($b = 1)) which sets $a and $b to 5 and 1 respectively and returns a value of the last argument (i.e. 1).
After ++'s you get 6-2.
refer to http://sillythingsthatmatter.in/PHP/operators.php for good examples