Comparative explanation of the three major flow control statements in PHP

PHP has three major process controls: sequence control, branch control, and loop control.

1. Sequential control: The program is executed step by step from top to next in order.

2. Branch control: Selective execution of the program. It is also divided into single branch, multiple branches, and multiple branches.

a. Single branch: basic syntax structure:

if(条件表达式){
　　语句;
　　//.....;
}

Tips: No matter how complex the conditional expression is, it will ultimately be true or false;

Example,

a=11;
if(a>10){
　　echo "a>10";
}

b. Multiple branches: basic syntax:

if(条件表达式){
　　语句;
　　//.....;
}else{
　　语句;
　　//.....;
}

c. Multiple branches: basic syntax:

if(条件表达式){
　　语句;n个语句;
}else if(条件表达式){
语句;n个语句;
}elseif(条件表达式){
语句;n个语句;
}eles{
语句;n个语句;
}

Tips: 1. else if can be One can also have multiple. 2. The last else may not have

d, switch branch statement

switch(表达式){　　case 常量1:
　　　　语句;n个语句;
　　　　break;
　　case 常量2:
　　　　语句;n个语句;
　　　　break;
　　case 常量3:
　　　　语句;n个语句;
　　　　break;
　　default:
　　　　语句;n个语句;
　　　　break;}

Note:
1. There may be one or more case statements
2. Defaul statement may not exist (according to your own code Business logic)
3. Usually, after the case statement, break is required to indicate Exit switch statement
4. The type of constant (int, float, String, Boolean)

Key points: The program is first configured in case order. If none is matched, the contents of the default statement will be executed until break is encountered, and then the switch will exit;

Comparison of if and switch branches:
if judges a certain range, while switch judges a point, so we can choose them like this:
Application scenario: When the branch is a few When there is a point (such as determining the direction of a tank), use switch.
When the branch is a judgment of several areas (range), consider using if.

Loop control process

for(循环初值; 循环的条件; 步长){
//n多语句;
}

while(循环条件){
//循环体 ,语句
}

do{
//循环体
}while(循环条件);

According to normal thinking, we should ensure that when accepting data, $_REQUEST['parameter'] must match the html element name given on the submission data page. Be consistent. If they are inconsistent, a notice will appear. At the same time, the data we accept is null, which is equivalent to "".

//$_REQUEST This method can accept the user's post or get request data

break and continue

Loop-related statements-break

Basic concept: indicates the end of the current for, while, do..while, switch, process, you can give a number, Indicates which layer to exit to.

$i=0;
while(++$i){
switch($i){
case 5:
echo quit at5
;
break;
case 10:
echo quitat 10
;
break 2;
default:
break;
}
}
echo '$i='.$i;

The result is:

quit at 5
quit at 10
$i=10

From the above case, we get several conclusions:

1. The break statement jumps out of layer 1 by default

2. The number after the break statement cannot exceed the actual number of loop levels that can be jumped out, otherwise, a fatalerror will be reported

Loop related statements-continue

Basic Concept : continue is used to end the remaining code of this cycle and start a new cycle from scratch (if the condition is true, continue execution), continue can also be followed by a number to indicate the number of cycles to restart from

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