Things to note for newbies on the road PHP newbies on the road (4)

Getting Started with PHP
4.1 Data Types
PHP supports integers, floating point numbers, strings, arrays and objects. Variable types are usually not determined by the programmer but by the PHP runtime (what a relief!). Of course, if you like, you can also use cast or the function settype() to convert a variable of a certain type into a specified type.
Numeric value
　The numerical type can be an integer or a floating point number. You can use the following statements to assign a value to a value:
$a = 1234; # Decimal number
$a = -123; # Negative number
$a = 0123; # Octal number (equal to 83 in decimal)
$a = 0x12; # Hexadecimal number (equal to 18 decimal numbers)
$a = 1.234; # Floating point number "double precision number"
$a = 1.2e3; # Exponential form of double precision number
String
　Strings can A field definition enclosed in single or double quotes. Note that the difference is that strings enclosed in single quotes are defined literally, while strings enclosed in double quotes can be expanded. Moreover, you can use backslash () in a double-quoted string to add escape sequences and conversion characters to the string. For example:
$first = 'Hello';
$second = "World";
$full1 = "$first $second"; # Generate Hello World
$full2 = '$first $second'; # Generate $first $ second
$full3="01DC studio,." 2000 copyright." " ;
Please note the last line. If you need to use double quotes in the string, you can use the backslash character, as shown in this line of statement. The backslash here is used to change the functionality of double quotes.
　Characters and numbers can be connected using arithmetic symbols. Characters are converted to numbers using their original position. There are detailed examples in the PHP manual.
Arrays and Hash Tables
　 Arrays and hash tables are supported in the same way. How you use them depends on how you define them. You can define them using list() or array(), or assign values ​​to arrays directly. The index of the array starts from 0. Although I haven't explained it here, you can easily use multidimensional arrays.
// An array containing two elements
$a[0] = "first";
$a[1] = "second";
$a[] = "third"; // Simple way to add array elements
// Now $a[2] is assigned the value "third"
echo count($a); // Print out 3 because the array has 3 elements
// Define an array with one statement and assign the value
$myphonebook = array (
"sbabu" => "5348",
"keith" => "4829",
"carole" => "4533"
);
// Oh, forget about the dean, let Let's add an element
$myphonebook["dean"] = "5397";
// The carale element you defined is wrong, let's correct it
$myphonebook["carole"] => "4522"
// Me Haven't you been told how to use similar support for arrays? Let's take a look
echo "$myphonebook[0]"; // sbabu
echo "$myphonebook[1]"; // 5348
Some other useful functions for arrays or hash tables include sort(), next( ), prev() and each().
Object
Use the new statement to generate an object:
class foo
{
function do_foo ()
{
echo "Doing foo.";
}
}
$bar = new foo;
$bar->do_foo() ;
Change variable type
　 It is mentioned in the PHP manual: "PHP does not support (and does not require) defining the variable type directly when declaring the variable; the variable type will be determined based on the situation in which it is used. If you assign the variable var to a String, then it becomes a string. If you assign an integer value to it, then it becomes an integer. "
$foo = "0"; // $foo is a string (ASCII 48).
$foo++; // $foo is the string "1" (ASCII 49)
$foo += 1; // $foo is now an integer (2)
$foo = $foo + 1.3; // $foo is a Double precision number (3.3)
$foo = 5 + "10 Little Piggies"; // $foo is an integer (15)
$foo = 5 + "10 Small Pigs"; // $foo is an integer (15)
If you want to forcefully convert the variable type, you can use the same function settype() as in C language.
4.2 Variables and Constants
You may have noticed that variables are prefixed with a dollar sign ($). All variables are local variables. In order to use external variables in the defined function, use the global statement. And if you want to limit the scope of the variable to the function, use the static statement.
$g_var = 1; // Global scope
function test()
{
global $g_var; // This way you can declare global variables
}
　More advanced is the variable representation of variables. Please refer to the PHP manual. This can sometimes be useful.
　PHP has many built-in defined variables. You can also use the define function to define your own constants, such as define("CONSTANT", "value").
4.3 Operators
　 PHP has the commonly seen operators in C, C++ and Java. The precedence of these operators is also consistent. Assignment also uses "=".
Arithmetic and characters
　There is only one operator related to characters:
$a + $b: Add
$a - $b: Subtract
$a * $b: Multiply
$a / $b: Divide
$ a % $b: Modulo (remainder)
$a. $b: String concatenation
Logical and comparison
Logical operators are:
$a || $b: or
$a or $b: or
$a && $b: Same as
$a and $b: Same as
$a xor $b: XOR (true when $a or $b is true, false when both are the same)
! ​​$a: Non-
comparison The operators are:
$a == $b: equal to
$a != $b: not equal to
$a < $b: less than
$a <= $b: less than or equal to
$a > $b : Greater than
$a >= $b : Greater than or equal to
Like C, PHP also has a triple operator (?:). Bit operators also exist in PHP.
Priority
Just like C and Java!
4.4 Control process structure
　PHP has the same process control as C. I will briefly introduce it below.
if, else, elseif, if(): endif
if (expression one)
{
. . .
}
elseif (expression two)
{
. . .
}
else
{
. . .
}
// Or like Python
if (expression one) :
. . .
. . .
elseif (expression two) :
. . .
else :
. . .
endif ;
Loops. while, do..while, for
while (expression)
{
. . .
}
do
{
. . .
}
while (expression);
for (expression one; expression two; Expression 3)
{
. . .
}
//Or like Python
while (expr):
. . .
endwhile;
switch
switch is the best replacement for multiple if-elseif-else structures ：
switch ($i)
{
case 0:
print "i equals 0";
case 1:
print "i equals 1";
case 2:
print "i equals 2";
}
break, continue
break interrupts the current loop control structure.
continue is used to jump out of the remaining current loop and continue executing the next loop.
require, include
　Just like #include preprocessing in C. The file you specify in require will replace its location in the main file. When referencing a file conditionally, you can use include(). This allows you to split complex PHP files into multiple files and reference them separately when needed.
4.5 Function
　You can define your own function like the following example. The return value of the function can be any data type:
function foo (variable name one, variable name two, . . . , variable name n)
{
echo "Example function.n";
return $retval;
}
　All PHP code can appear in function definitions, even in definitions of other functions and classes. Functions must be defined before being referenced.
4.6 Class
　Use the class model to create classes. You can refer to the detailed explanation of classes in the PHP manual.
class Employee
{
var $empno; // Number of employees
var $empnm; // Employee name
function add_employee($in_num, $in_name)
{
$this->empno = $in_num;
$this- >empnm = $in_name;
}
function show()
{
echo "$this->empno, $this->empnm";
return;
}
function changenm($in_name)
{
$ this->empnm = $in_name;
}
}
$sbabu = new Employee;
$sbabu->add_employee(10,"sbabu");
$sbabu->changenm("babu");
$ sbabu->show();

The above has introduced the precautions for newbies on the road to PHP (4), including the precautions for novices on the road. I hope it will be helpful to friends who are interested in PHP tutorials.