Basic tutorials on various process controls in PHP

ConditionsControl statementsThere are four main types of if, if...else, elseif and switch. while loop is the simplest loop statement in PHP. Use The break/continue statement breaks out of the loop.

1. if

if () {
    statement;
} else if {
    statement;
} elseif {
    statement;
} else {
    statement;
}

else The meanings of if and elseif syntax analysis are slightly different, but the bottom line is that they will produce exactly the same behavior

2. Loop

while () {
    statement;
}
do {
    statement;
} while();
for (;;) {
    statement;
}
foreach (as) {
    statement;
}
break、continue

can accept an optional numeric parameter to decide how many loops to jump out of

3. switch

switch () {
    case :
        statement;
    default:
        statement;
}

allows the use of semicolon instead of after the case statement Colon

switch ($beer) {
    case 'tuborg';
    case 'carlsberg';
    case 'heineken';
        echo 'Good choice';
    break;
    default;
        echo 'Please make a new selection...';
    break;
}

4, declare

declare structure is used to set the execution instructions of a piece of code.

Currently, we only know two instructions: ticks and encoding

5, Ticks

Tick (clock cycle) is a code that the interpreter executes every N times in the declare code segment. Low-level statements that time events as they occur. The value of N is specified with ticks=N in the directive part of declare

Not all statements can be timed. Usually conditions expressions and parameter expressions are not timeable.

tick represents an event. The definition of the event is in register_tick_function, and the execution frequency of the event is (ticks=n).

Purpose, trigger an event every few statements executed, such as recording events. This allows you to check the execution speed of the PHP code within declare. You can find the location of the code segment where the slower part occurs.

<?php
    function doTicks ()
    {
        echo &#39;Ticks&#39;;
    }
    register_tick_function(&#39;doTicks&#39;);
    declare(ticks = 1) {
        for ($x = 1; $x < 10; ++ $x) {
            echo $x * $x . &#39;<br />&#39;;
        }
    }
?>

Operation result:

1
TicksTicks4
TicksTicks9
TicksTicks16
TicksTicks25
TicksTicks36
TicksTicks49
TicksTicks64
TicksTicks81
TicksTicksTicksTicks

First of all, the complete for loop is counted as a statement, but it must wait until the end of the loop, so the echo in the for loop is compiled at compile time Count the first statement.

So the first doTicks is executed after the first echo, that is, the first tick event occurs after 1 is output.

The for loop in x=9 also ends. This is another statement, outputting the second ticks; the loop of $x=10 starts, but the loop condition is no longer met. The for loop execution ends, this loop is another statement, and the third ticks are output.

Finally, declare itself is also a statement, so the fourth ticks are output.

6, Encoding

You can use the encoding directive to specify the encoding method for each script

<?php
declare(encoding=&#39;ISO-8859-1&#39;);
// code here
?>

7, reutrn

require, include,require_once, include_once

require and include are almost identical, except for the way failure is handled. require generates an E_COMPILE_ERROR level error when an error occurs, in other words it will cause the script to abort while include only generates a warning (E_WARNING) and the script will continue to run.

8. goto

The goto operator can be used to jump to another location in the program. The target position can be marked with the target name followed by a colon, and the jump instruction is the goto followed by the mark of the target position.

Goto in PHP has certain restrictions. The target location can only be in the same file and scope, which means that it cannot jump out of a function or class method, nor can it jump into another function. It also cannot jump into any loop or switch structure. You can jump out of a loop or switch. The usual usage is to use goto instead of multiple levels of break.

<?php
goto a;
echo &#39;Foo&#39;;
a:
echo &#39;Bar&#39;;
?>

The above is the detailed content of Basic tutorials on various process controls in PHP. For more information, please follow other related articles on the PHP Chinese website!