PHP for While Loop statement Learning Note _php Tutorial

This article is to introduce the basic use of circular statements in PHP, including for Loop, while loop and do While loop use method, this article is very suitable for beginners PHP beginner Oh.

Use the For statement to control multiple variables, enabling advanced applications for multiple loops.

Here is a program that outputs the 9*9 multiplication table with a for statement:

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for ($i =1; $i <=9; $i + +) { for ($j =1; $j <= $i; $j + +) { $sum = $i * $J; echo $sum. " T "; } echo " "; } ?>

In addition to the while Loop statement mentioned earlier, PHP provides the same functionality for a For loop statement. The For statement can implement a more complex and multifunctional loop, and any while loop can be replaced by a for loop.

Basic structure form:

for (expression 1; expression 2; expression 3) {
Execute Statement Body
}

The following procedures are performed:

1, first execute the expression 1;

2, then judge the true and false expression 2, if False, jump out for the next PHP statement for the loop, if True then enter for loop execution statement body;

3, then executes the expression 3;

4, return to the 2nd step cycle operation;

5. Jump out of the for statement until the loop ends.

Flow chart:

Instance:

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for ($i =0; $i <=9; $i + +) { $sum + = $i; echo $sum. " T "; } ?>

The Do...while Loop statement is a variant of the while loop, which functions like while, but checks that the expression is true after it executes the loop, and the basic structure is:

do{;
Statement body
}while (expression)
The Do...while Loop statement executes the statement body once, then evaluates the condition of the expression, returns the loop once if the value is true, and then jumps out of circulation for false.

Instance:

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$i = 1; $sum = 0; do{ $sum + = $i; echo $sum. " n "; $i + +; }while ($i <=10) ?>

While Loop statement
The while statement is a statement used by PHP to implement loops, with the following basic structure:

while (judgment statement) {
Execution statement body;
}
A judgment statement is usually judged by relational or logical operators.

The statement body is executed when the judgment statement is true, and then the value of the expression is checked, and if it is still true, the execution statement is executed again. Exits the loop until the judgment statement is false.

Instance:

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$i = 0; while ($i <9) { $i + +; echo $i. " "; } ?>

The difference between while and Do...while:

The main difference between the two is that the first loop of the Do...while statement must be executed.

If the two loop bodies execute the same statements, they will run the same results, but the results of both loops will be different when the expression is false at first.

Instance:

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/* While loop */ $a = 9; while ($a >10) { echo "enters the" while Loop statement body "; } /* Do...while Cycle */ do{ echo "enters Do...while loop statement body"; }while ($a >10) ?>

PHP exits the loop with the break and Continu statements, and their role is to jump out of the loop when the condition is met.

Break Statement usage:
When the value of the condition is true, the entire loop is terminated prematurely, and the statement outside the loop is executed.

Instance:

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/* The output area is within 100 of the circular area */ for ($r = 1;; $r + +) { $A =3.14* $r * $R; if ($A >50) break; /* Form a dead loop if there is no break */ echo $A. " "; } ?>

Continue statement usage:
The function of the continue statement is to end the loop and go to the next loop, not to exit the entire loop program.

Instance:

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/* Output within 10 odd */ for ($i =1; $i <=10; $i + +) { if ($i%2==0) continue; echo $i. " T "; } ?>

The difference between break and Continue statements:

As we can see from the above example, the effect of break and continue statements in exiting a loop is fundamentally different.

Continue just ends this cycle, and then returns to the loop body to continue the next cycle;

Break terminates the entire loop immediately and does not repeat.

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