The second day of learning PHP in ten days_PHP tutorial

Learning purpose: Master the process control of PHP

1. There are three structures of if..else loops

The first one is to use only the if condition and treat it as a simple judgment. Interpreted as "what to do if something happens". The syntax is as follows:

if (expr) { statement }

where expr is the condition for judgment, usually using logical operation symbols as the condition for judgment. The statement is the execution part of the program that meets the conditions. If the program has only one line, the curly brackets {} can be omitted.

Example: This example omits the curly brackets.

if ($state==1)echo "Haha" ;
?>

What’s important to note here is that judging whether they are equal is == Instead of =, ASP programmers may often make this mistake, = is assignment.

Example: The execution part of this example has three lines, and the curly brackets cannot be omitted.

if ($state==1) {
echo "Haha;
echo "
" ;
}
?>

The second type is to add an else condition in addition to if, which can be interpreted as "what to do if something happens, otherwise how to solve it" The syntax is as follows

<.> if (expr) { statement1 } else { statement2 } Example: Modify the above example into a more complete process. Since there is only one line of instructions for execution, there is no need to add curly brackets

if ($state==1) {
echo "haha" ;
echo "
";
}
else{
echo "haha";
echo "
";
}
?>

The third type is the recursive if..else loop, which is usually used in various decision-making situations. Combine several if..else and apply them

See the example below

if ( $a > $b ) {
echo "a is bigger than b" ;
} elseif ( $a == $b ) {
echo "a is equal to b" ;
} else {
echo "a is smaller than b" ;
}
?>
The above example only uses a two-level if..else loop to compare the two variables a and b. This kind of recursive if..else loop is actually used. , please use it with caution, because too many layers of loops can easily cause problems in the design logic, or missing braces, etc., will cause inexplicable problems in the program

2. There is only one kind of for loop. , no change, its syntax is as follows

for (expr1; expr2; expr3) { statement }

where expr1 is the initial value of the condition and expr2 is the condition for judgment, which is usually used. Logical operators are the conditions for judgment. expr3 is the part to be executed after executing the statement. It is used to change the conditions for the next loop judgment, such as adding one, etc. The statement is the execution part of the program that meets the conditions. If the program has only one line, the curly brackets {} can be omitted.

The following example is written using a for loop.

for ( $i = 1 ; $i <= 10 ; $i ++) {
echo "This is the ".$i."th loop< ;br>" ;
}
?>
3. The switch loop usually handles compound conditional judgments. Each sub-condition is part of the case instruction. In practice, if many similar if instructions are used, it can be synthesized 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 a variable name. The exprN after case usually represents the variable value. After the colon is the part to be executed that meets the condition. Be sure to use break to break out of the loop.

switch ( date ( "D" )) {
case "Mon" :
echo "Today is Monday" ;
break;
case "Tue" :
echo "Today is Tuesday" ;
break;
case "Wed" :
echo "Today is Wednesday" ;
break;
case "Thu" :
echo "Today is Thursday" ;
break;
case "Fri" :
echo "Today is Friday" ;
break;
default:
echo "Today is a holiday" ;
break;
}
?>
What needs to be noted here is break; don’t omit it, default, and omission is okay.

Obviously, using the if loop in the above example is very troublesome. Of course, when designing, you should put the conditions with the greatest probability of occurrence at the front and the conditions with the least occurrence at the end, which can increase the execution efficiency of the program. In the above example, since the probability of occurrence is the same every day, there is no need to pay attention to the order of the conditions.

That’s it for today. Let’s start talking about the use of database tomorrow.