Detailed explanation of php basic control structure examples

Control structure

If we want to effectively respond to user input, the code needs to be judgmental. The structure that allows the program to make judgments is called a condition.

1. if..elseLoopThere are three structures
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, usually the logical operator is 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.

<?php 
if ($state==1)echo "哈哈" ; 
?>

Special attention here is that == is used to determine whether they are equal, not =. ASP programmers may often make this mistake, = is an assignment.
Example: The execution part of this example has three lines, and the curly brackets cannot be omitted.

<?php 
if ($state==1) { 
echo "哈哈 ; 
echo "<br>" ; 
} 
?>

The second type is that in addition to if, an else condition is added, which can be interpreted as "how to deal with something if something happens, otherwise how to solve it." The syntax is as follows:
if (expr) { statement1 } 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.

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

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.
Look directly at the example below:

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

The above example only uses a second-level if..else loop to compare the 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 missing braces, etc., can cause inexplicable problems in the program.

2, for loopThere is only one type, no change, its syntax is as follows:
for (expr1; expr2; expr3) { statement }
expr1 among them 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:

<?php 
for ( $i = 1 ; $i <= 10 ; $i ++) { 
echo "这是第".$i."次循环<br>" ; 
} 
?>

3. Switch loop usually handles compound conditional judgment. 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:
switch (expr) { case expr1: statement1; break; case expr2: statement2; break; default: statementN; break; }
The expr condition is usually the variable name say. The exprN after case usually represents the variable value. After the colon is the part to be executed that meets the condition. Be sure to use break to break out of the loop.

<?php 
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; 
} 
?>

What you need to pay attention to 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, the conditions with the greatest probability of occurrence should be placed 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.

The above is the detailed content of Detailed explanation of php basic control structure examples. For more information, please follow other related articles on the PHP Chinese website!