Introduction to the use of PHP loop functions - PHP basic introductory tutorial_php basics

Loops in PHP basically execute the same block of code a specified number of times.

There are four main types of PHP loops: while, do...while, for, and foreach. Below we explain the usage of each loop separately.

while statement:

As long as the specified condition is true, the code block will be executed in a loop.

Format:

while(expr)
{
statement;
}

Semantics: First judge expr, if the expression expr is false, then end; if the expression expr is true, execute the statement statement, and judge expr again after the execution is completed. If the expression expr is still true, continue to execute the statement statement; until The expression expr is false and ends.
Example:

The above example demonstrates a loop. As long as the variable i is less than or equal to 5, the code will continue to execute in a loop. Each time the loop loops, the variable will be incremented by 1, and then the value of i will be entered;

do…while statement:

First execute the code block once, and then repeat the loop when the specified condition is true.
Format:

do{
statement;
}

while(expr) semantics: First execute the statement statement once, and then judge expr. If the expression expr is false, it ends; if the expression expr is true, continue to execute the statement statement in a loop, and judge expr again after the execution. If If the expression expr is still true, the statement statement continues to be executed; until the expression expr is false, it ends.

Note: The difference between it and while is that do...while executes the statement once without any judgment for the first time, and then judges whether the condition is true. It should be noted here that the others are the same as while.
Example:

The above example demonstrates a loop. I assign a value of 6 to variable i. Obviously, this is not true compared with the condition in while, but the result is 6, which is the do...while statement mentioned before. It is the first No judgment is made this time. It is executed once and then judged whether the condition is true.

for statement

: If you have determined the number of times a block of code will be repeated, you can use a for statement.
Grammar

for (initialization; condition; increment)
{
code to be executed;
}

Semantics: The for statement has three parameters. The first parameter initializes the variable, the second parameter holds the condition, and the third parameter contains the increment required to execute the loop. If multiple variables are included in the initialization or increment parameter, they need to be separated by commas. And the condition must evaluate to true or false.
Example:

The following example will display the text "Hello World!" 5 times:

foreach statement: The foreach statement is used to loop through an array.

Each time through the loop, the value of the current array element will be assigned to the value variable (the array pointer will move one by one) - and so on.
Grammar

foreach (array as value)
{
code to be executed;
}

Example
The following example demonstrates a loop that can output the values ​​of a given array:

Explanation: First I define an array arr, and then I use foreach to loop, where ($arr as $value) means assigning the value in the $arr array to $value, and then executing the statement to output $value value.
The output result is:

one
two
three