What data must I check in PHP and how?

I hope you know the golden rule that every and each PHP programmer must know.

The First Rule

Check all data received from user!

All the data that we've got in the global arrays such as $_POST and $_GET must be checked.

Use filter_input() method to delete not needed symbols.

There are some types of filters for this method. Some useful examples:

$name = filter_input(INPUT_GET, 'name', FILTER_SANITIZE_STRING);
$email = filter_input(INPUT_GET, 'email', FILTER_SANITIZE_EMAIL);

There is one more rule.

The Second Rule

How to compare strings in Java

String in Java is not a primitive type, such as integer, boolean etc.
Every string is an object.
We can compare strings using method equals() or the identity operator ==.
Let's separate between the two types of comparing here.

• While using equals() the comparison is done by characters. String name1 = "Hello, world!";
String name2 = "Hello, world!";
if (name1.equals(name2))
    System.out.println("The names are the same.");
// Output "The names are the same."
  That means string "Hello, world!" is equal to the second "Hello, world!", because these strings have the same characters.
• While using == the pointers to strings are compared. if (name1 == name2)
    System.out.println("The names are the same.");
else
    System.out.println("Oh, no!"); // Output "Oh, no!" When we write this code:
  String name1 = "Hello, world!"; we have this picture in the main memory:
  
  The variable name1 holds the address of object in the memory (in our example the address is 42).
  name1 is a pointer to the location in memory where the object is held.
  
  Let's create strings as different objects.

How to compare float numbers safely?

This short article explains why we cannot use "==" to compare floats and how to compare floats right.
You can try to run this code in Java to understand the problem. double a = 1.0f / 3.0f;
double b = a + a + a;

System.out.println(a); // Output 0.3333333432674408
System.out.println(b); // Output 1.0000000298023224
System.out.println(1 == b); // Output false

Why?

If the compared values are the results of computation, they can be not equal.
Binary representation of the number 1/3 cannot be precise, because the place where the number is stored is limited. So the number rounding was made: 1/3 = 0.333.. = 0.(3) = 0.3333333432674408
So we have b = 1.0000000298023224 that is not equal to 1.0;

How to get round that problem?

How to replace string in the project using terminal in Ubuntu?

We want to replace the string "regexp" with the string "replacement" in the terminal.
Let's say our project path is /home/www/project_name.
Actually regexp string is a regular expression pattern for our string.

This command works right:
cd /home/www/project_name
find . -type f -print0 | xargs -0 sed -i 's/regexp/replacement/g' Let's see what the command means.
I will translate it to the normal language for human beings.

Go to my project folder:
cd /home/www/project_name Find all files (-type f) in my project folder:
find . -type f Use \0 delimiter (and not whitespace) to separate between the found pathnames in the output.
(We don't want whitespaces, because filenames can contain whitespaces and we will not be able to separate between pathnames).
-print0 This is a pipe. It means all the output that we have got before this sign "|" becomes an input for a next command (xargs in our case).
| xargs takes the output (pathnames that the command find found).
We use -0 because pathnames are terminated by \0 (instead of by whitespace). We know because we specified (find -print0).
xargs -0 sed - stream editor for filtering and transforming text.
-i allows to edit files in place.
-g replace all matches, not just the first match.
Replace our "regexp" with "replacement". sed -i 's/regexp/replacement/g'

What do lazy and greedy regular expressions mean?

Greedy expression tries to get as much as possible.
If you write a regular expression like this

<.+>

for the string:

<p>My expression</p>

you will get all the string

<p>My expression</p>

Oh, yes.. this thing is really greedy.

Let's take a look at the lazy one. If you write a regular expression like

<.+?>

We have just added "?". That means we want the smallest possible group. Now we have this result:

<p>

Here you are. The laziest thing you have ever seen :)

What screen resolution should I use for my web page design?

Not so long ago the answer was - 1024 x 768.
But you know, "the times they are changing".
Browser Display Statistics shows:

Today, most visitors have a screen resolution higher than 1024x768 pixels.

Of course you should know your audience and make the decision about resolution accordingly.