PHP Self-study Note 3

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Add
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When defining constants, it is recommended to determine whether a constant name is defined, to be judged by defined (), and to return a Boolean type
if (!defined ("POEM")) {//Not defined
Define ("POEM", "Du Fu");
}
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1, operator
2. Select structure
3. Cyclic structure
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1, operator
Arithmetic operations (+-*/non-divisible% for remainder + +)--)
$x = 10;
$y = $x + +; After the first assignment, the self-increment
$z =++ $x; Self-increment and assign value first
Echo $y, $x, $z;
Logical operations
With && and OR | | Or not! Not XOR different or
Note: (1) Priority: and less than &&,or less than | |
$e =false| | True
$f =false or true;//first assignment, then judge
echo $e, "----", $f; 1---
Suggested use of && or | |, add parentheses as needed when using or or
(2)
Expression 1&& Expression 2 if 1 is false, no longer judge 2
Expression 1| | Expression 2 If 1 is true, no longer judge 2
$x = 10;
$y = 9;
$z = $x | | + + $y;//Left is 1, right + + $y not executed
Echo $z, $y;
Comparison operators
> < >= <=
= = (value equal) = = = Congruent (both values and types are equal)
! = (unequal values)!== not congruent (value or type not equal)
$x = 10;
$y = 10.0;
$z = 9;
if ($x = = $y) {//value, etc.
echo "Equal 1";
}
if ($x = = = $y) {//value and type are exactly equal and
echo "equivalent 2";
}
if ($x! = $z) {
echo "Unequal 3";
}
！ (A and b) =!a | | ！ B

if ($x!== $z) {//value or type varies
echo "Unequal 4";
}
"Note" string comparison: compare each character from left to right

Assignment operators
=      +=  -=  *=  /=  %=   .=
$a = 10;
$a +=12;
echo $a;

$y = "Hello";
$y. = "World";
Echo $y;

Trinocular operation (ternary expression)
Conditions? Expression 1: Expression 2
If the condition is true, the result is an expression of 1, otherwise the result is an expression of 2
Requirement: If you enter Tom 123 to log on successfully, the login fails
$name =$_get["username"];
$PSW =$_get["PSW"];

$result = $name = = "Tom" && $psw = = "123"? " Login successful, $name, $PSW ":" Login Failed ";
$result 2= $name = = "Tom" && $PSW! = "123"? " The password is incorrect ":" ";
$result 3= $name! = "Tom"? User does not exist ":" ";

Echo $result, $result 2, $result 3;
The second Kind
$result =$_get["User"]== "Tom"? ($_get["Pass"]== "123"? "Login Successful": "Password is incorrect"): "User name does not exist";
echo $result;

Select structure
Single Branch If
Double if Else
Multi-Branch If else if ... else

echo Date ("Y year M D Day D week");
$time =date ("H");
if ($time <12) {
echo "Good Morning";
}else if ($time >=12&& $time <18) {
echo "Good Afternoon";
}else{
echo "Good evening";
}
**SWITCH selection Structure
Multiple choices: values, etc. or unequal, cannot handle the selection of range or interval
$time =$_get["Time"];
Switch ($time) {
Case "1": echo "Monday"; Break
Case "2": echo "Tuesday"; Break
Case "3": echo "Wednesday"; Break
Case "4": Echo "Week 4"; Break
Case "5": Echo "Week 5"; Break
Case "6": Echo "Week 6"; Break
Case "7": echo "Sunday"; Break
Default:echo "Week error";
}


$time = 4;
Switch ($time) {
Case "1": echo "Monday";
Case "2": echo "Tuesday";
Case "3": echo "Wednesday"; Break
Case "4": Echo "Week 4";
Case "5": Echo "Week 5"; Break
Case "6": Echo "Week 6";
Case "7": echo "Sunday";
Default:echo "Week error";
}
Week 4 Week 5
"Note" When the switch matches case succeeds, the selection structure is not exited until a break is encountered, so it is recommended to add a break after each case;
Default position arbitrary, execution is also encountered break exit selection structure
Switch execution order: matches the case first, and matches the default if it does not match successfully
Example 1:
$b =true;
Switch ($b) {
Case False:echo ' false ';
Case 0:echo ' ******* ';
Case Null:echo ' empty ';
Case-1:echo ' negative ';
Case 2:echo ' Tuesday ';
Default:echo "no This Day";
}
Match a case entry that is not false when the expression is true in switch
Not 0 is true, false and 0, and Null is False
Example two:
$b = 2;
Switch ($b) {
Case True:echo ' happy ';
Case 2:echo ' Tuesday ';
Default:echo "no This Day";
}
Description: If a case is true, the entry will match until the match succeeds.
Example three:
$b = "2";
Switch ($b) {
Case 2:echo ' Tuesday ';
Case True:echo ' happy ';
Default:echo "no This Day";
}
Case matching is numeric, switch structure can automatically convert type
Example four:
$b =null;
Switch ($b) {
Case False:echo ' false ';
Case Null:echo ' null object ';
Default:echo "no This Day";
}
Description: The expression value in switch is null as a false match
Here null and false are match entries, and the results are related to the order of the two case portals
Loop structure
while (condition) {
Loop body
Note: Control variables
}
Requirements: For 1-100 and
$i =1;//Control variables
$sum =0;//Save Results
while ($i <=100) {
$sum + = $i;
$i ++;//, don't forget.
}
Echo $sum;
Do-while: Xianzhanhouzou
do{
Loop body
modifying control variables
}while (conditions);

Requirements: For 1-100 and
$i =1;//Control variables
$sum =0;//Save Results
do{
$sum + = $i;
$i + +;
}while ($i <=100);
Echo $sum;
For loop
for (statement 1; condition; statement) {
Loop body
}
Requirements: For 1-100 and
$sum =0;//Save Results
for ($i =1; $i <=100; $i + +) {
$sum + = $i;
}
Echo $sum;
Note: When the number of cycles is known, a for loop is usually used, and if you do not know the number of cycles generally use while or do-while
Cyclic structure Complex
Outer control line number
for ($i =1; $i <=9; $i + +) {
The inner control loses several # of each line
for ($j =1; $j <= $i; $j + +) {
echo "#";
}
echo "<br>";
}

Outer control line number
for ($i =1; $i <=9; $i + +) {
The inner layer controls what is entered on each line
Lose space
for ($j =1; $j <=10-$i; $j + +) {
echo "&nbsp;&nbsp;";
}
Output
for ($j =1; $j <= $i; $j + +) {
echo "#";
}
echo "<br>";
}
Output pyramid
for ($i =1; $i <=9; $i + +) {
The inner layer controls what is entered on each line
Lose space
for ($j =1; $j <=10-$i; $j + +) {
echo "$";
}
Output
for ($j =1; $j <=2* $i-1; $j + +) {
echo "#";
}
echo "<br>";
}
Output Hollow Pyramid
for ($i =1; $i <=9; $i + +) {
The inner layer controls what is entered on each line
Lose space
for ($j =1; $j <=9-$i; $j + +) {
echo "&nbsp;";
}
Output
for ($j =1; $j <=2* $i-1; $j + +) {
Except for the last line,//Output # on the first end, otherwise the output space
if ($i!=9) {
if ($j ==1| | $j ==2* $i-1) {
echo "#";
}else{
echo "&nbsp;";
}
}else{
echo "#";
}
}
echo "<br>";
}

PHP Self-study Note 3