Some basics (1/3) Variables, tables, functions and procedures

Upon request of beginers, some basic information to better understand...

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Questions - Variables - Tables - Functions - Procedures

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Variables

They are containers enabling to store information that is reusable in multiple positions in code

• Statement: To select the name of a variable you must :
  1. Check that this name is available (key word or variable of language) ;
  2. That the name in embedded with letter, figures or _ (underscore) ;
  3. That the first character is NOT capital letter ;
  4. With PHP enter the symbol $ in front of the first letter.
  
  
• Allocation : We use the symbol = to fill in a container with data:
  

  myvar_1 = "hello"		$myvar_1 = "hello";	put the string "hello" in the variable
  myvar_2 = 250		$myvar_2 = 250;	put the number 250 in the variable
  myvar_3 = true		$myvar_3 = true;	put the value true in the variable
  myvar_4 = myvar_2		$myvar_4 = $myvar_2;	put in the myvar_4 variable the value included in the variable myvar_2

  
  
• Categories : So, you understand that you cannot reserve the the same memory space to put in storage a number and a long chain of characters... Also, the language needs to know the kind of information that a variable contains.... Each variable is classified when first built-in; it means the kind of information stored in the variable is primarily determined... Be aware of any mistake you can enhance if you do not respect this rule!
  
  
• Read : A data in a container is readable just by mentioning its name
  For example, if you want to post: <% = myvar_1 %> or <? echo $myvar_1; ?>
  
  
• Operations : We can, obviously, build the content of a variable in a different and smarter way... Some examples:
  

  myvar_1 = "bon" & "jour"		$myvar_1 = "bon"."jour";	Concatenation of two strings
  myvar_2 = 50*5		$myvar_2 = 50*5;	Arithmetic + - * /
  myvar_3 = (myvar_2 = 250)		$myvar_3 = ($myvar_2==250);	Comparison = (== en PHP) > >= < <= <> (!= en PHP)
  myvar_2 = myvar_2 + 12 myvar_1 = myvar_1 & " Didier"		$myvar_2 += 12; $myvar_1 .= " Didier";	Modification .= += -= ... in PHP

  
  
  
• Dynamic variables: Sometimes, it could be better to store (or build) a variable within another variable ... And, we will develop as follow to read its content:
  

  <% truc_fr = "Bienvenue" truc_en = "Welcome" lang = "fr" execute "response.write truc_" & lang %>		<? $truc_fr = "Bienvenue"; $truc_en = "Welcome"; $lang = "fr"; echo ${"truc_".$lang}; // display Bienvenue ?>

  
  
• PHP 4 allows assign values to variables based on reference...
  Just put a & before the name of a variable... an example :
  
  

  <? $var_1 = "Essai"; echo $var_1; // display Essai $var_2 = &$var_1; echo $var_2; // display Essai $var_1 = "Test"; echo $var_2; // display Test ! $var_2 = "Try"; echo $var_1; // display Try ! ?>

  
  And, if you want to get more about references...