Detailed explanation of several methods of PHP loop control statements_PHP tutorial

In PHP, loop statements generally use while, for, and foreach, and control statements are if swicth. Let me introduce to you how to use PHP loop control statements.

1. There are three structures of if..else loops. The first one only uses the if condition and treats it as a simple judgment.

Interpreted as "what to do if something happens".
The syntax is as follows: if (expr) {statement} where expr is the condition for judgment. Logical operation symbols are usually used as the condition for judgment.
The statement is the execution part of the program that meets the conditions. If the program has only one line, the curly brackets {} can be omitted.
Example: This example omits the curly braces.

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if（＄state==1） echo"哈哈"; ?>

if（＄state==1）

echo "Haha";
?>

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if（＄state==1）{ echo"哈哈; echo" "; } ?>

Special attention here is that == is used to determine whether they are equal, not =. ASP programmers may often make this mistake, = is assignment.

Example: The execution part of this example has three lines, and the curly brackets cannot be omitted.

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if（＄state==1）{

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if（expr）{ statement1 }else{ statement2 }

echo"Haha;

echo"
";
}

?>

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if（＄state==1）{ echo"哈哈"; echo" "; }else{ echo"呵呵"; echo" "; } ?>

The second type is to add an else condition in addition to if, which can be interpreted as "what to do if something happens, otherwise how to solve it."
The syntax is as follows:

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if（expr）{ statement1

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if（＄a>＄b）{ echo"a比b大"; }elseif（＄a==＄b）{ echo"a等于b"; }else{ echo"a比b小"; } ?>

}else{ statement2 }

Example: Modify the above example into a more complete process. Since there is only one line of instructions for executing else, there is no need to add braces.

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if（＄state==1）{ echo "Haha"; echo" "; }else{ echo "Hehe"; echo" "; } ?>

The third type is the recursive if..else loop, which is usually used in various decision-making judgments. It combines several if..else for processing. Just look at the example below

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if（＼a>＄b）{ echo "a is bigger than b"; }elseif（＄a==＄b）{ echo "a equals b"; }else{ echo "a is smaller than b"; } ?>

The above example only uses a two-level if..else loop to compare two variables a and b.
When actually using this kind of recursive if..else loop, please use it with caution, because too many levels of loops can easily cause problems in the design logic, or if there are too few braces, etc., it will cause inexplicable problems in the program.
2. There is only one type of for loop with no changes. Its syntax is as follows
for（expr1;expr2;expr3）{statement}
where expr1 is the initial value of the condition.
expr2 is the condition for judgment, and logical operators are usually used as the condition for judgment.
expr3 is the part to be executed after executing the statement. It is used to change the conditions for the next loop judgment, such as adding one, etc.
The statement is the execution part of the program that meets the conditions. If the program has only one line, the curly brackets {} can be omitted.
The following example is written using a for loop.

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for（＄i=1;＄i ）{ echo"这是第".＄i."次循环 "; } ?>

for（＄i=1;＄i ){
echo"This is the ".$i."th loop
"; }

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switch（expr）{ caseexpr1: statement1; break; caseexpr2: statement2; break; default: statementN; break; }

?>

3. The switch loop usually handles compound conditional judgments. Each sub-condition is part of the case instruction.
In practice, if many similar if instructions are used, they can be synthesized into a switch loop. The syntax is as follows

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switch(expr){ caseexpr1:

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switch（date（"D"））{ case"Mon": echo"今天星期一"; break; case"Tue": echo"今天星期二"; break; case"Wed": echo"今天星期三"; break; case"Thu": echo"今天星期四"; break; case"Fri": echo"今天星期五"; break; default: echo"今天放假"; break; } ?>

statement1;

break;
caseexpr2:
statement2;
break;
default:

statementN;

break; }

The expr condition is usually the variable name. The exprN after case usually represents the variable value.

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While循环是php中最简单的循环语句，他的语法格式是： While (expression){ statement; }

After the colon is the part to be executed that meets the condition. Be sure to use break to break out of the loop.

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switch(date("D")){ case"Mon": echo "Today is Monday"; break; case"Tue": echo "Today is Tuesday"; break; case"Wed": echo "Today is Wednesday"; break; case"Thu": echo "Today is Thursday"; break; case"Fri": echo "Today is Friday"; break; default: echo "I have a holiday today"; break; } ?>

What needs to be noted here is break; Don’t omit it, default, it’s okay to omit it. Obviously, using the if loop in the above example is very troublesome. Of course, when designing, you should put the conditions with the greatest probability of occurrence at the front and the conditions with the least occurrence at the end, which can increase the execution efficiency of the program. In the above example, since the probability of occurrence is the same every day, there is no need to pay attention to the order of the conditions. php loop control statement 1. While statement

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While loop is the simplest loop statement in PHP , his grammatical format is: While (expression){ statement; }

When the value of expression is true, the statement statement will be executed. After the execution is completed, it will return to expression to continue judgment. The loop is not broken out until the expression evaluates to false.
Example:

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$num = 1; $str = “10以内的偶数为：”; while($num if($num % 2 == 0){ $str.=$num.”"; } $num++; } echo $str; ?>

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$num = 1; $str = "Even numbers within 10 are:";
while($num if($num % 2 == 0){
$str.=$num.””;
}
$num++;
} echo $str;
?>

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For循环是php中最复杂的循环结构，它的语法格式为： For(expression1;expression2;expression3){ statement; }

2. Do...While statement

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$num=1; for($i=1;$i $num *=$i; } echo $num; ?>

While statement also has another form of expression, Do...While. The syntax is:

Do{ statement;
}While(expression); The difference between the two is that the Do...While statement loops one more time than the While statement.
When the value of the While expression is false, the While loop jumps out of the current loop directly, while the Do...While statement executes the program block first and then evaluates the expression.

3. For statement

For(expression1;expression2;expression3){

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$arr=array(“We”,”are”,”the”,”best”,”team”,”!”); if(is_array($arr) == true){ foreach($arr as $key => $value){ echo $key.”=”.$value.” ”; } }else{ echo”该变量不是数组，不能使用foreach语句”; } ?>

For loop is the most complex loop structure in PHP , its syntax format is:

statement; } Among them: expression1 takes the value once unconditionally during the first loop. expression2 is evaluated before each loop starts. If the value is true, the statement is executed; otherwise, the loop is jumped out and execution continues. expression3 is executed after each loop. Example:

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$num=1; for($i=1;$i $num *=$i; } echo $num; ?> 4. Foreach statement Foreach loop was introduced in php4.0 and can only be used for arrays. In php5, support for objects has been added. The syntax format of this statement is: foreach(array_expression as $value) statement; or Foreach(array_expression as $key => $value) statement; The Foreach statement will traverse the array array_expression. Each time it loops, the value in the current array is assigned to $value (or the table below the array is assigned to $key and the corresponding array value is assigned to $value). At the same time, the array pointer is moved backward. Move, and cycle like this repeatedly until the traversal is completed. When using the Foreach statement, the array pointer is automatically reset, so there is no need to manually set the pointer position. Example

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$arr=array("We","are","the","best","team","!"); if(is_array($arr) == true){ foreach($arr as $key => $value){ echo $key.”=”.$value.” ”; } }else{ echo "This variable is not an array and the foreach statement cannot be used"; } ?> http://www.bkjia.com/PHPjc/632683.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/632683.htmlTechArticleIn php, loop statements generally use while, for, foreach and control statements are if swicth. Below I Let me introduce to you how to use PHP loop control statements. 1. The if..else loop has...