In php, loop statements include many, such as for, foreach, while, do while, and goto statements. Below I will give you a brief introduction to the structure and usage of these loop statements.
For Loop Control
For (initial cyclic values; cyclic conditions; step size ){
// Execute the statement;
}
Example
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FOR ($ I = 0; $ I <= 2; $ I ++) |
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Output Value
Value is now 0
Value is now 1
Value is now 2
In the first loop, $ I = 0, which means the expression ($ I <= 2) is true. Therefore, when the print statement is executed, $ I is incremented by 1 to 1.
In the second loop, $ = 1, which means the expression ($ I <= 2) is true. Therefore, when the print statement is executed, $ I is incremented by 1 to 2.
In the third iteration, $ I = 2, which means the expression ($ I <= 2) is true. Therefore, when the print statement is executed, $ I increments to 1 3.
In the fourth iteration, $ I = 3, which means the expression ($ I <= 2) is false. Therefore, PHP does not execute loops or print statements.
While Loop
The basic syntax structure is
While (loop condition ){
// Execute the statement;
// The value of the cyclic condition changes. If this parameter is not added, it will become an endless loop.
}
Example
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<Html> <body> |
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Let's just give a simple example. In the following example, the while LOOP statement is used. It means that when the variable $ a is less than or equal to 5, a loop is executed, and a join statement is executed in this loop, the first is to output the value of $ a, and the second is to add 1 to the value of $ a until $ a is less than or equal to 5 is FALSE, that is, $ a> 5 is used to stop the loop.
Do... while loop control
Basic syntax structure
Do {
// Execute the statement;
// The value of the cyclic condition changes. If this parameter is not added, it will become an endless loop.
} While (Cyclic condition );
Example
In this example, run a loop first, that is, add $ I to 1, and then output the value of $ I. After the first loop is executed, check the condition $ I <5, if the condition is met, execute another loop until $ I <5 is FALSE.
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<Html> <body> |
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Loop-related statement-break
Basic concept: end the current for, while, do... while, switch, flow, you can give a number, indicating to exit to the layer.
1. The break statement jumps out of Layer 1 by default.
2. The number next to the break statement cannot exceed the number of loops that can actually jump out. Otherwise, a fatal error is reported.
Loop-related statements-continue
Basic concept: continue is used to end the remaining code of this loop. It starts a new loop (if the condition is true, it will continue to be executed) and can be followed by a number, indicates the number of cycles to start again.
Goto statement
Basic concept: Through the goto statement, we can jump the program to a specified place for execution.
Goto tag;
Statement;
Quick Start case:
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Goto; Echo 'a '; A: Echo 'bb '; |
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Constants in php
Note:
Constants can be understood as special variables:
1. No need before defining constants $
2. Once a constant is defined, its value cannot be modified.
3. When defining a constant, it needs to assign an initial value.
4. constants can be defined through define or const.
5. Constant names, which are generally in upper case and separated by underscores
6. When to use constants: if we do not want a value to change in the program, consider using constants, such as the circumference rate and tax rate ....
Quick Start case:
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<? Php
Define ("TAX_RATE", 0.08 ); // Method 2 (php5.3) Const TAX_RATE2 = 0.1; ?> |
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