I am in the making of some code that needs to check if a users login details are correct, and I therefore need a lot of if-statements inside each other. If any of the conditions in the if-statements are not true, they should alle return the same value. Is there an easy way of doing this, instead of writing the same multiple times? I have made an example below to visualize my problem. As you can see here I write " else { return false; }" multiple time, and this is what I am wondering if you are able to do more efficiently. Maybe so I only have to write "or else return false" once.
//some code
if (/*some condition*/) {
//some code
if (/*some new condition*/) {
//some code
if (/*some new condition*/) {
//some code
} else {
return false;
}
} else {
return false;
}
} else {
return false;
}
I am having a hard time finding a good way to explain my problem, so if you have a more elegant way of explaining it, do not hesitate to edit my post. I am also not quite sure that the title is as good as it could be, so if you have any ideas to an alternativ please say so :)
Lets say you have something like that (I added No):
if ( condition1 ) {
//some code 1
if ( condition2 ) {
//some code 2
if ( condition3 ) {
//some code 3
} else {
return false;
}
} else {
return false;
}
} else {
return false;
}
Since each time a condition is false, you exit the function returning false, you can directly test if the condition is false using a negation (if the negated condition is true):
if ( !condition1 ) {
return false;
}
//some code 1
if ( !condition2 ) {
return false;
}
//some code 2
if ( !condition3 ) {
return false;
}
//some code 3
This doesn't reduce the number of if statements, but you avoid many nesting levels and the else statements.
You can also try the switch statement. For many situations it will produce cleaner code.
<?php
if ($i == 0) {
echo "i equals 0";
} elseif ($i == 1) {
echo "i equals 1";
} elseif ($i == 2) {
echo "i equals 2";
}
switch ($i) {
case 0:
echo "i equals 0";
break;
case 1:
echo "i equals 1";
break;
case 2:
echo "i equals 2";
break;
}
?>
The switch statement is also compatible with using strings:
<?php
switch ($i) {
case "apple":
echo "i is apple";
break;
case "bar":
echo "i is bar";
break;
case "cake":
echo "i is cake";
break;
}
?>
Good luck! :)
Related
in PHP (and even other languages but in the present case this is more for PHP), i often end up sometimes having to code long conditions such as the example below:
i have a code with many conditions and i want to display a different result based on certain conditions.
if something is RED and the other thing is RED, then print X,
if something is RED but the other thing is BLACK, then print Y
if something RED and the other thing is RED but a third thing is blue, then print X
& so on
is there a way to properly handle this by using some kind of data structure/configuration array/matrix/whatever ? that is, storing these "conditions" and "results" properly in some kind of configuration array or other ?
instead of having to code nested conditions that can be tricky to support afterwards
like this very small example but in a much bigger scale
if (preg_match(/something/, $string) {
$result = 'GREEN';
} elseif (preg_match(/something/, $string) {
$result = 'RED';
} else {
if (something else) {
$result = 'GREEN';
} else {
if (something OR something) {
$result = 'AMBER';
} else {
$result = 'GREEN';
}
}
}
or is it the only way of handling this ?
maybe with a single
if (something and something or something) {
} elseif (something and something and something) {
} elseif (something and something or something and something) {
} etc
thank you for your help
i'm coding an app that should display a different "status" for a certain data depending on many different data (other attributes of this data), and i'd like to avoid having unreadable code
You can use nested arrays:
$conditions = [
'/something1/' => [
'/something2/' => "X"
],
'thing3' => [
'/thing3/' => 'Y',
'/thing4/' => 'Z'
]
];
$matched = false;
foreach ($conditions as $key1 => $val1) {
if (preg_match($key1, $string)) {
if (is_array($val1)) {
foreach ($val1 as $key2 => $val2) {
if (preg_match($key2, $string)) {
$result = $val2;
$matched = true;
break;
}
}
} else {
$result = $val1;
$matched = true;
}
}
if ($matched) {
break;
}
}
if (!$matched) {
$result = 'default';
}
To allow arbitrary levels of nesting you could turn this into a recursive function.
For the purposes of the answer below I'm assuming you're coding OO PHP.
One variable
When I have one variable that determines the outcome, if the variable is boolean or close to being boolean (meaning it can only either be one or two different values), is to use an if() statement like you have. If the variable can be a variety of (known) values, like your colours example, I use a switch() function.
Two or more variables
If I have two variables that determine the outcome, for instance colour and size, I first use a switch(), then for each switch, I use a method that contains another switch().
It may be more verbose, but it is so much easier to keep track of in the long run. Below is a simplified example of the logic.
switch ($colour) {
case 'red':
red_handler($size);
break;
case 'green':
green_handler($size);
break;
case 'blue':
blue_handler($size);
break;
}
/** We already know the first variable value is red */
function red_handler($size)
{
switch ($size) {
case 'small':
echo "my fruit is a cherry";
break;
case 'medium':
echo "my fruit is an apple";
break;
case 'large':
echo "my fruit is a watermelon";
break;
}
}
In a similar vein to #dearsina i'd tend to separate it out into functions for this kind of thing, for example if you know there are lots of cases where it could return the same value, e.g.:
if(isGreen($string)) return 'GREEN';
else if (isRed($string)) return 'RED';
function isGreen($string) {
if(cond1)return true;
if(cond2 && cond3)return true;
if(cond4 || cond 5)return true;
return false;
}
function isRed($string) {
if(cond6)return true;
if(cond1 && cond7)return true;
if(cond2 || cond 8)return true;
return false;
}
we do sometimes use the style you've suggested...
if (something and something or something) {
} else if (something and something and something) {
but you can quickly end up back in the same problems of readability and maintenance issues
Is there any way in PHP to return at else of first statement, if the second statement which is inside of first, is false
if($first == true) {
//other code which is not necessary to mention here!
if($second == true){
// do smth
}
else{
return to the else of $first statement
}
//other code which is not necessary to mention here!
}
else{
//do smth else
}
Yes, there are multiple ways. For starters, just combine both the statements and give another condition:
if ($first == true && $second == true) {
// do smth
} elseif ($first == true && $second == false) {
// else of$first statement
} else {
//do smth else
}
This can be used as a guidance to get an idea to start. But if you can get a real world example, there can be conditions grouped, tailored to your requirement.
While there is no native way to jump to outer elses from an inner else, but you can set a flag for later processing:
$do_else = false;
if($first == true) {
//other code which is not necessary to mention here!
if($second == true){
// do smth
}
else{
$do_else = true;
}
//other code which is not necessary to mention here!
}
else{
$do_else = true;
//do smth else
}
if($do_else){
//do smth else
}
If the answers above doesn t help you in the real situation, you can create a function for execute in 'else' statements to avoid code duplication
I need to implement 3 'if conditions' in my script, i've looked it up online but I can only find solutions up to 2 if's like below
<?
if (condition 1){
do something;
}
elseif (condition 2){
do something else;
}
else {
do this last;
}
?>
but I would need something like this:
if (condition 1) { do this };
else if (condition 2) {do that};
or else if (condition 3) {do that};
else (do this)
How do I go about this?
simply
if(condition){
}
else if(condition){
}
else if(condition){
}
else{
}
you can use switch case statements too. you can use else if as many as you want. Each condition inside if() can accept OR and AND operators as || for OR and && for AND you can use.
if (condition 1) { do this
} else if (condition 2) {do that
} else if (condition 3) {do that
} else { do this }
alternatively if you want to check one variable each time you can use a switch for example
$myvar = 5;
switch($myvar){
case 1:
//do this
break;
case 2:
//do that
break;
case 3:
//do that
break;
default:
//do this
}
You can use this construction
if ( $a == $b ) {
// something...
} else if ( $a == $c ) {
// something...
} else if ( $a == $d ) {
// something...
} else {
// otherwise...
}
But if all of the conditions are ( $a equals to something ) it's better to use switch ... case:
switch ( $a ) {
case $b:
// something...
break;
case $c:
// something...
break;
case $d:
// something...
break;
default:
// otherwise...
break;
}
Solution 1
Using many elseif statements as you want.
Use this solution when your conditions are complex, or comparing different variables.
if (/*condition 1*/) {
// Action to condition 1
} else if (/*condition 2*/) {
// Action to condition 2
} else if (/*condition 3*/) {
// Action to condition 3
} else if (/*condition n*/) {
// Action to condition n
} else {
// Action when no conditions match.
}
Solution 2
Using switch statement:
Use this condition when you want to compare a variable against constant values:
switch ($age) {
case 0:
return 'You are a baby';
break;
case 18:
return 'You are 18 years old';
break;
case 21:
case 22:
case 23:
return 'You are too old';
default:
return 'Unexpected age :(';
}
How about using the or operator, ||:
if (condition 1) { do this }
else if (condition 2 || condition 3) {do that}
else {do this}
An example:
<?php
function testCondition($a, $b) {
if ($a == $b) {
print ("They are the same<br />\n");
}
else if ($a == "a" || $b == "b") {
print ("One is the same as its letter<br />\n");
}
else {
print ("They are some other sort<br />\n");
}
}
testCondition("c","c");
testCondition("a","c");
testCondition("a","b");
testCondition("d","e");
?>
Outputs:
They are the same
One is the same as its letter
One is the same as its letter
They are some other sort
I have the same problem as first stated here. I have four variables but the second one is skipped and only 1,3, and 4 work. Why?
if(empty($fromName) or empty($fromEmail) or empty($subject) or empty($comments)) {
echo 'You cannot submit the form with empty fields. Please correct the form and resubmit.';
return false;
}
elseif($fieldDelete == "Delete this text!"){
echo "Delete the contents of the fourth field before submitting.";
return false;
}
elseif (($fromName == "Curtisvien") || ($fromName == "Thomastymn") || ($fromName == "RichardMark")) {
echo "Failed. Please try again.";
return false;
}
else {
$flgchk = mail ("$to", "$subject", "$message", "$headers");
$imgfile = "images/NatMap logo2.gif";
$handle = fopen($filename, "r");
$imgbinary = fread(fopen($imgfile, "r"), filesize($imgfile));
echo '<img src="data:image/gif;base64,' . base64_encode($imgbinary) . '" width=427 height=72 />';
echo "\n<br />\n<br />Thank You! An e-mail has been sent to the National Map web team and they will get back to you in the next 24-48 hours.";
}`enter code here`
I am just wondering if there is better way to solve my situatuion:
I have 6 independent variables to check. But if any of conditions is true it shouldnt check other. Normally I would write:
if (cond1 ) {
statement
} else {
if ( cond2 ) {
statement
} else {
if (cond3) {
statement
} else {
...
}
}
}
Surely you would admit it doesnt look good or it is not easy to read although it works. Do you know any other ways to write such if statement maybe using other notation or functions (switch? while?)
Yes, you can do
if (cond1 ) {
statement
} elseif ( cond2 ) {
statement
} elseif ( cond3 ) {
statement
}
See documentation
A more stylish way:
if(cond1):
statement1
elseif(cond2):
statement2
elseif(cond3):
statement3
elseif(cond4):
statement4
elseif(cond5):
statement5
elseif(cond6):
statement6
endif;
This is how you do it with a switch():
$a = 10;
$b = 100;
switch(true){
case ($a > $b):
echo 'a is bigger than b';break;
case ($b > $a):
echo 'b is bigger than a';break;
}
if (cond1 ) {
statement
} else {
if ( cond2 ) {
statement
} else {
if (cond3) {
statement
} else {
...
}
}
}
Change to:
if (Cond1){
}elseif (cond2){
}elseif (cond3){
}
Let's take a look at the following code:
if ($a == 1) {
echo "this is stage 1";
}
else if ($a == 2) {
echo "this is stage 2";
}
else if ($a == 3) {
$a = 1;
// at this point I want something that restarts the if-else construct so
// that the output will be "this is stage 1"
}
I'm working on an if else construct at the moment and let's say that I have three stages and the if-else construct checks which stage I'm in.
Now it happens that some activities in stage 3 lead to a jump back to stage 1. Now I've already passed the code for stage one, which is why I want to somehow restart the if-else construct. Is there a way to do that? And even more important: Is there a better way to do what I want? Because my idea doesn't seem to be good practice.
You're right, it's bad practice.
You're asking for goto.
Example:
<?php
goto a;
echo 'Foo';
a:
echo 'Bar';
The above would never output 'Foo'
It's difficult to suggest the better method without seeing exactly what you're trying to do, but consider a switch.
switch ($a) {
case 3:
// Execute 3 stuff
// No break so it'll continue to 1
case 1:
// Execute 1 stuff
break // Don't go any further
case 2:
// 2 stuff
break;
}
That's probably not what you want either.
You may just want to abstract the code into functions and call them multiple times if necessary.
You can put an endless loop around your if and break out if you're done
while (1) {
if ($a == 1) {
echo "this is stage 1";
break;
}
else if ($a == 2) {
echo "this is stage 2";
break;
}
else if ($a == 3) {
$a = 1;
}
else {
break;
}
}
Maybe you want to look at Wikipedia - Finite-state machine and this question PHP state machine framework
The short answer is yes, there is a way, but the better answer is yes to your second question as well.
Put, at very least, the code that can get called from multiple locations in a function. For example,
function stageOneCode() {
//do stuff;
}
etc.. I would recommend a function for each stage, but it's hard to make recommendations without actually seeing what's being executed in the stages.
In any event, at the end of your stage three function, simply call your stage one function.
A recursive function is helpful for this (but maybe overkill if it will always revert back to 1)
function echo_stage($stage) {
if ($a == 1) {
return "this is stage 1";
}
else if ($a == 2) {
return "this is stage 2";
}
return echo_stage(1);
}
echo echo_stage(5);
Or:
switch ($number)
{
case 2 :
echo "this is stage 2";
break;
case 1:
default:
echo "this is stage 1"
}
use switch(). you can have a "default" case as well as specific cases.
A loop is what you are searching for:
// initialize $a
$a = 1;
// the while loop will return endless
while (true);
// if you want to break for any reason use the
// break statement:
// if ($whatever) {
// break;
// }
if ($a == 1) {
echo "this is stage 1";
}
else if ($a == 2) {
echo "this is stage 2";
}
else if ($a == 3) {
$a = 1;
// continue will go back to the head
// of the loop (step 1) early:
continue;
}
// don't forget to increment $a in every loop
$a++;
}