PHP logical structures and conditional statements

With the continuous development of the Internet, PHP, as a powerful programming language, has become the favorite of Web developers. As a high-level programming language, PHP not only supports object-oriented programming, but also has a series of logical structures and conditional statements, providing programmers with many convenient and fast programming ideas.

Logical structure refers to the process of forming a complete program from basic program statements according to certain rules. In PHP, logical structures are delimited using curly braces {}, making the code clearer and easier to read. Common logical structures include sequential structures, selection structures, and loop structures.

Sequential structure means that the program is executed step by step in a certain order. In PHP, code is executed in a sequential structure by default. For example, we can write the following code:

$a = 1;
$b = 2;
$c = $a + $b;
echo $c;

The above code is a simple sequential structure. It consists of three statements, which are executed step by step in order, and finally the value of the variable $c is output.

The selection structure means that the program needs to choose different execution paths based on certain conditions during execution. In PHP, the selection structure is mainly implemented through if statements, if else statements, and switch case statements.

The syntax of the if statement is as follows:

if (条件表达式) {
    要执行的代码块
}

Sample code:

$age = 20;
if ($age >= 18) {
    echo "您已经成年了！";
}

The above code first creates a variable $age, and then uses the if statement to determine whether $age is greater than or equal to 18. If true, output "You are an adult!".

The syntax of the if else statement is as follows:

if (条件表达式) {
    要执行的代码块1
} else {
    要执行的代码块2
}

Sample code:

$age = 17;
if ($age >= 18) {
    echo "您已经成年了！";
} else {
    echo "您还未成年！";
}

The above code outputs different results according to the value of the variable $age.

The syntax of the switch case statement is as follows:

switch(变量或表达式) {
    case 值1:
        要执行的代码块1
        break;
    case 值2:
        要执行的代码块2
        break;
    default:
        要执行的代码块3
}

Sample code:

$x = 1;
switch ($x) {
    case 1:
        echo "星期一";
        break;
    case 2:
        echo "星期二";
        break;
    default:
        echo "不是星期一或星期二";
}

The above code defines a variable $x, and outputs the corresponding value according to the value of $x through the switch case statement day of the week.

The loop structure means that the program needs to execute a certain piece of code multiple times. In PHP, loop structures are mainly implemented through for loops, while loops, and do while loops.

The syntax of the for loop is as follows:

for (初始化表达式; 条件表达式; 递增表达式) {
    要执行的代码块
}

Sample code:

for ($i = 1; $i <= 10; $i++) {
    echo $i;
}

The above code will loop from 1 to 10 and output the value of $i in each loop.

The syntax of the while loop is as follows:

while (条件表达式) {
    要执行的代码块
}

Sample code:

$i = 1;
while ($i <= 10) {
    echo $i;
    $i++;
}

The above code has the same effect as the for loop. It will also loop from 1 to 10, and each time Output the value of $i in the loop.

The syntax of the do while loop is as follows:

do {
    要执行的代码块
} while (条件表达式);

Sample code:

$i = 1;
do {
    echo $i;
    $i++;
} while ($i <= 10);

The above code will also loop from 1 to 10, and output $i in each loop value.

To sum up, the logical structures and conditional statements in PHP provide programmers with rich programming ideas and flexible code implementation methods. Whether it is a sequential structure, a selection structure or a loop structure, various complex functional requirements can be easily realized. Mastering these logical structures and conditional statements is an essential skill for web developers.

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