10 days to learn PHP the next day

Learning objectives: Mastering PHP's Process Control

1, If ... else loop has three kinds of structure

The first is to use only if conditions, as a simple judgment. Explained as "What to do if something happens". The syntax is as follows:

if (expr) {statement}

The condition that expr is judged is usually used as the criterion of logic operation symbol. and statement for the implementation of the conditions of the program, if the program has only one line, you can omit the curly braces {}.

Example: This example omits curly braces.

<?php
if ($state ==1) echo "haha";
?>

It is particularly noteworthy here that the decision whether equality is = = rather than =,asp programmer may make this error, = is assignment.

Example: The execution section of this example has three lines and cannot omit curly braces.

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


The first two, except if, plus the condition of else, can be explained as "What to do if something happens, how to deal with it". The syntax is as follows

if (expr) {statement1} else {Statement2} example: The above example is modified to more complete processing. Where else is due to only one row of instructions, so no curly braces are added.
<?php
if ($state ==1) {
echo "haha";
echo "<br>";
}
else{
echo "hehe";
echo "<br>";
}
?>


The third type is recursive if. else loops, usually used in a variety of decision judgments. It will be several if.. Else take to combine the use of processing.

Look directly at the example below

<?php
if ($a > $b) {
echo "A greater than B";
} elseif ($a = = $b) {
echo "a equals B";
} else {
echo "A is smaller than B";
}
?>

The previous example uses only the two-level if. else loop, to compare A and b two variables. You actually want to use this recursive if. else loop, please use caution, because too many layers of the loop can make the logic of the design problem, or less dozen curly braces, will cause the program to appear inexplicable problems.

2, for loop on pure only one, no change, its syntax is as follows

for (EXPR1; expr2; expr3) {statement}

Where the EXPR1 is the initial value of the condition. EXPR2 is the condition of judgment, which is usually judged by the logic operation symbol (logical operators). EXPR3 the part to be executed after the execution of statement to change the condition for the next round of judgment, such as add one. Wait a minute. and statement for the implementation of the conditions of the program, if the program has only one line, you can omit the curly braces {}.

The following example is an example written in the For loop.

<?php
for ($i = 1; $i <= $i + +) {
echo "This is the first". $i. " Secondary cycle <br> ";
}
?>

3, switch cycle, usually deal with the conditions of the compound judgment, each child condition, is the case instruction part. If you use many similar if instructions on the implementation, you can synthesize it 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, usually the variable name. The ExprN after the case usually represents the value of the variable. The colon is followed by the part that meets the condition. Notice that you want to jump off the loop with a break.

<?php
Switch (date ("D")) {
Case "Mon":
echo "Today Monday";
Break
Case "Tue":
echo "Today Tuesday";
Break
Case "Wed":
echo "Today Wednesday";
Break
Case "Thu":
echo "Today Thursday";
Break
Case "Fri":
echo "Today Friday";
Break
Default
echo "Today's Holiday";
Break
}
?>

Here is the need to pay attention to the break; do not omit, default, omit is OK.

Obviously, the example above is cumbersome with the IF loop. Of course, in the design, the most likely to have the highest probability of the first, the least occurrence of the conditions on the last side, you can increase the efficiency of the implementation of the program. The previous example has the same probability of appearing every day, so don't pay attention to the order of the conditions.

That's it for today, starting tomorrow with the use of the database.