What are the PHP control flow statements?

Whether it is PHP or other languages, a program always consists of several statements.

##There are three control statements in PHP to implement selection structures and loop structures:

1. Conditional control statements: if, else, elseif and switch;

2. Loop control statements: foreach, while, do while and for;

3. Transfer control statements: break, continue and return. (Recommended learning: PHP programming from entry to proficiency)

Conditional control statement:

If statement, usage:

If（A）
    Statement1；
Else
    Statement2；

Analysis: If A is true, execute statement1; otherwise, execute statement2.

Example, code:

<?php
 　$a = 59;　　//根据$a的值，判断是否及格。如果>=60则输出及格
　 if($a>=60){
　echo “及格”;
   }else
　　echo “不及格”;
?>

If···elseif···else statement, usage:

If(A)
 　 Statement1； 
Elseif(B)
 　 Statement2； 
Else
　Statement3;

Analysis: If A is TRUE, execute statement1. Otherwise, if the value of B is TRUE, then statement2; otherwise, execute statement3. Of course: if statements can also be nested.

The following is an example of If···elseif···else:

<?php
　　$a = 59;
　　if($a>=60)        //在大于等于60的情况里在进行分类
　{
　　if($a==100)
　　echo “满分”;
　　elseif($a>=90)
　　echo “优秀”;
　else
　　echo “及格”;
　}
　else
　　echo “不及格”;
　?>

Switch statement, the syntax is as follows:

Switch(A)
{
　Case val1:
　　Statement1;
　　Break;
　Case val2:
　　Statement2;
　　Break;
　Default:
　　Statement3;
}

When the value in a case statement When the value of switch expression A matches, PHP starts executing the statement until the end of the switch program segment or until the first break statement is encountered

(If break is not encountered, PHP will continue execution next case).

The following is an example without break:

<?php
　　switch($leve1)
　{
　　case 3:
　　　echo “高级”;
　　case 2:
　　     echo “中级”;
　    case 1:
　　　 echo “初级”;
　　default:
　　　 echo “错误的等级值”;
　}
　?>

What did you think of from this? ?

<?php
　　$level = 3;
　　switch($level)
　{
　　case 3:
　　　echo “赋予管理员权限”;
　　case 2:
   　echo “赋予站务权限”;
　　case 1:
   　　echo “赋予版主权限”;
　　default:
　　　echo “赋予普通用户权限”;
　}
　?>

Compared with if, switch achieves higher efficiency:

<?php
　　$a = 59;
　switch($a)
　　{
　case $a == 100;
　　echo “满分”;
　　break;
　case $a >= 90;
　　echo “优秀”;
　　break;
　case $a >= 60;
　　echo “及格”;
　　break;
　default:
　　echo “不及格”;
　}
　?>

So what is the loop statement used for? Of course it is used to perform an operation repeatedly.

While and do···while

While syntax:

While(A)
    Statement;

Analysis: as long as the while expression If A in the formula is TRUE, the statement is executed.

The syntax of do···while:

do
{
　　Statements;
　}
　while(A)

The difference between do···while and while is that do···while is checked at the end of the loop, regardless of the conditions of the loop Whether it is satisfied or not, do···while will be executed once.

For example:

<?php
　　$a = 5;          //先判断$a是否大于5，如果大于5则执行。
　　while($a>5)
　{
　　echo “This is  while.”;
　　$a–;
　}
　do               //先执行do之内的语句，然后进行判断。
　{
　　echo “This is do…while.”;
　　$a–;
　}
　while($a > 5)
　?>

For statement, syntax:

For(A；B；C)
    Statement;

Analysis: The first expression is executed unconditionally once at the beginning of the loop. Generally, A is an assignment statement; B is run before the loop starts. If it is TRUE,

continues the loop and executes the nested statements of the loop; C is executed after the loop, usually self-increment and self-decrement operations.

Code:

<?php
　　for($a = 5;$a > 5;$a–)；
　　echo “This is for”;
　?>

Foreach statement, used for array traversal, will be learned later.

Transfer control statements

There are three main types of transfer control statements in PHP: break, continue and return.

break statement

The break statement is used to end the current loop. break can accept an optional numeric parameter to determine how many loops to jump out of.

Example:

　<?php
　　$a = 5;
　　$b = 10;
　while($a <100)   //$a<100开始循环
　{
　　echo “a = “.$a.”<BR>”;  //输出$a，“.”时连接运算符，相当于java中的“+”
　while($b > 0)           //$b>0，开始循环
　{
　　echo “b = ” .$b.”<BR>”;  //输出$b
　　$b–;
　　if($b == 3 )                 //如果$b==3，则跳出while($b>0)
　　break;              
　}
　　$a++;
　　if($a == 30)
　　break;           //如果$a==30,就跳出while($a<100)
　}
　?>

Continue statement

Continue is used to jump out of this loop. Different from break, continue will continue to execute the next loop after jumping out.

Return statement The Return statement is used to end a function or a script file. If the return statement is called in a function, it will immediately end the execution of the function and return its value as a parameter.

Of course, return can also be used as a function in PHP. Such as return(), and write the parameters to be returned in parentheses. This usage is uncommon.

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