Some unconventional usage of for loop statements in PHP. The syntax of the for statement php (as the mainstream development language) is defined as follows: for (expr1; expr2; expr3) statement. The following describes several useful variants of the for statement. 1. the syntax of php (as the for statement php (as the mainstream development language) is defined as follows:
For (expr1; expr2; expr3)
Statement
The following describes several useful variants of the for statement.
1. php (as the mainstream development language) FOR infinite loops
The first is an infinite loop (also known as an "endless loop "). The null expression is effective in syntax, so we can leave the three expressions of the for statement empty, which will produce continuous execution of the for nested statement.
<? Php (as the mainstream development language)
For (;;){
// Place the statements that require continuous execution
}
?>
Although some tasks use infinite loops, most Program tasks, especially php (as the mainstream development language), can be involved, when an infinite loop is used, some conditions for terminating the loop are added.
<? Php (as the mainstream development language)
For (;;){
// If it is 2199 AD, it will jump out of the loop
If (date ('Y') = '000000 '){
Break;
}
}
?>
2. php (as the mainstream development language) FOR using null expressions
Next we will talk about the use of the null syntax in the initialization statement expr1. The most common function of leaving expr1 blank is to complete more complex initialization.
<? Php (as the mainstream development language)
If (isset ($ I )){
Unset ($ I );
If (int) date ('') <2008 ){
$ I = 0;
} Else {
$ I = 1;
}
} Else {
$ I = 3;
}
For (; $ I <10; $ I ++ ){
Echo $ I;
}
?>
In the same way, the iteration expression expr3 may also be left blank. you can also use this to write more complex iterations, such as calling different iterations based on different conditions.
The expr2 field in the for statement is an infinite loop mentioned above. of course, you can add more complex conditions to determine when to jump out of the loop, which is not repeated here.
3. php (as the mainstream development language) FOR multiple loops
Using multiple loops to control multiple variables is also a feature that is often ignored in the for statement. In the following example, a double loop is usually used in a general task, and a triple or above loop is of little significance.
<? Php (as the mainstream development language)
For ($ I = 0, $ j = 10; $ I <= 10; $ I ++, $ j --){
Echo "$ I + $ j = 10 ";
}
?>
The above code will be output:
0 + 10 = 10
1 + 9 = 10
2 + 8 = 10
3 + 7 = 10
4 + 6 = 10
5 + 5 = 10
6 + 4 = 10
7 + 3 = 10
8 + 2 = 10
9 + 1 = 10
10 + 0 = 10
4. php (as the mainstream development language) FOR more complex expressions
If the three expressions of the for statement are more complex, they can be used to optimize the algorithm. You can even use a for statement without a loop body to complete some tasks. For example, calculation of accumulation or factorial:
<? Php (as the mainstream development language)
// Calculates the accumulate result from 1-5, and returns the value to $ j.
For ($ I = 1, $ j = 0; $ I <= 5; $ j + = $ I ++ );
Echo $ j;
// Calculate the factorial result from 1-5. the bin value is $ j.
For ($ I = 1, $ j = 1; $ I <= 5; $ j * = $ I ++ );
Echo $ j;
?>
Syntax is defined in the for (expr1; expr2; expr3) statement as follows. 1. php (...
