PHP study notes (3) Operators and control structures

PHP study notes (3) Operators and control structures_PHP tutorial

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Release： 2016-07-21 15:25:43

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1. String Insertion
To provide developers with maximum flexibility in handling string values, PHP provides
a method for literal insertion and content insertion.
Double quotes provide maximum flexibility because variables and transfer sequences are parsed accordingly.

Copy code The code is as follows:

$userName = "Zhang San"; 
 echo "His name is $userName "; 
echo "
"; 
//There will be some problems in Chinese
echo "His name is $userName. He is 19 years old. Grow up! "; 
echo "
"; 
//Can be solved by string concatenation
echo "His name is ".$userName.", he He is 19 years old and has grown up! " 
//Escape characters can be parsed
echo "Although there are many girls on his QQ account, n none of them belong to him"; 
?> ; 

Some commonly used escape characters
Escape sequence description
n Line feed character
r Carriage return
t Horizontal tab
\ Backslash
$ dollar sign
" Double quotes

Single quotes will be interpreted as declared. When parsing the string, variables and escape sequences will not be parsed.
echo 'Wu Qi The variable name is: $userName, the escape character n is invalid in single quotes'
?>
2. Operator
operator is used to operate on arrays and variables Symbols for certain operations.
Arithmetic operator
Composite assignment operator
Preincrement and decrement and postincrement and decrement operators:
$a=++$b;
$ a=$b++;
$a=--$b;
$a=$b--;
Comparison operator
Example of operator name
+ Add $a+$b
- Subtract $a-$b
* Multiply $a*$b
/ Divide $a/$b
% and take the remainder $a%$b
Using the operator is equivalent to
+= $a+=$b $a=$a+$b
-= $a-=$b $a=$a-$b
*= $a*=$b $a= $a*$b
/= $a/=$b $a=$a/$b
%= $a%=$b $a=$a%$b
.= $a .=$b $a=$a.$b
Usage method of operator name

= = equal to $a= =$b
= = = identical $a= = =$b
!= Not equal to $a!=$b
!= = Not equal to $a!= =$b
<> Not equal to $a<>$b
< Less than $a<$b
> Greater than $a>$b
<= Less than or equal to $a<=$b
>= Greater than or equal to $a>=$b

Note: Identity means that true will be returned only if the operands on both sides are equal and the data types are also the same;
For example: 0= ="0" This returns true because the operands are equal
0= = ="0" This returns false because the data types are different

Logical operator
! Not! $b
If $b is false, then
returns true; otherwise the opposite
&& with $a&&$b
If $a and $b are both
true, the result is true;
otherwise it is false
|| or $a||$b
if $ When one
of a and $b is true or both are
true, the result is
true; otherwise, it is false
and is the same as $a and $b
and &&, but Its priority
is lower
or or $a or $b
is the same as ||, but its priority
is lower

operators "and" and "or "has a lower priority than && and ||.
Ternary operator
Condition ? value if true : value if false
Example: ($grade>=50 ? "Passed" : "Failed")

Error suppression Operator:
$a=@(57/0);
The divisor cannot be 0, and an error will occur, so add @ to avoid error warnings.
Array operator
+ union!$b
returns an array containing all elements
in
$a and $b
= = equivalent to $a&&$b
If $a and $b have
the same elements, return
true
= = = Identity $a||$b
If $a and $b have
the same elements and
are in the same order, return
true
!= non-equivalent $a and $b
If $a and $b are not
equivalent, return true
< ;> Non-equivalent
If $a and $b are not
equivalent, return true
!= = Non-identical $a or $b
If $a and $b are not
Identity, returns true

Priority and associativity of operators:
Generally speaking, operators have a set of priorities, which is the order in which they are executed. The
operator is also associative, that is, the execution order of operators with the same priority. This order is usually from
left to right, right to left or irrelevant.
The table of operator precedence is given below. The top operator has the lowest priority, and the priority increases in order from top to bottom in the table.

Operator Precedence
Left,
Left Or
Left Xor
Left And
Right Print
Left
= += -= *= / = .= %= &= |= ^= ~= <<=
>>=
Left? :
left||
left&&
left|
left^
left&
irrelevant = = != = = = = != =
irrelevant< <= >>=
Left<< >>
Left + - .
Left* / %
Right
! ~ ++ --
(int)(double)(string)(array)(object) @
right[]
Irrelevant New
Irrelevant()
In order to avoid priority confusion, you can use parentheses to avoid priority class.
3. Control Structure
If we want to effectively respond to user input, the code needs to be judgmental. The structure that allows the program to judge
is called a condition.
if
Conditional judgment statement
if (conditional judgment){
//...
}
if (conditional judgment){
//.. ..
}
else {
//....
}
if (conditional judgment) {
//...
}
Left| |
left&&
left |
left^
left&
irrelevant = = != = = = = != =
irrelevant<<= >> ;=
Left<< >>
Left + - .
Left* / %
Right
! ~ ++ --
(int)(double) (string)(array)(object) @
right[]
Not relevant New
Irrelevant

elseif {
//...
}
elseif {
//....
}
else {
//....
}
switch
Statement
switch (variable) {
case "value 1":
//...
break;
case "value 2":
//...
break;
case "value N ":
//...
break;
default:
//....
break;
}
while
loop
while (Condition) {
//....
}
for
Loop
for (initial value; condition; counter) {
//....
}
In addition to the for loop, PHP also provides the foreach loop, which is specifically used for the use of arrays. We cover it in detail in the
group.
do
while
Loop
do {
//...
} while(condition);
If you want to stop the execution of a piece of code, according to what you need to achieve The effects are different and can be achieved in 3 ways.

The first one: break; exit the loop; the second one is exit; exit the program; the third one is continue; exit the current loop
loop
if (condition)
{
break; //continue
}