Strengthen the for loop

The for loop is open bounded. Its general form is: for(; ; ) statement; initialization is always an assignment statement, which is used to assign initial values ​​to loop control variables; conditions The expression is a relational expression that determines when to exit the loop; the increment defines how the loop control variable changes after each loop. These three parts are separated by ";". For example: for(i=1; i<=10; i++) statement; In the above example, "i" is first assigned an initial value of 1, and it is judged whether "i" is less than or equal to 10. If so, the statement is executed, and then the value is increased by 1. Then re-judge until the condition is false, that is, when i>10, the loop ends.

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Points to note
Strengthen the for loop
For loop in PHP
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Points to note

1. The statement in the for loop can be a statement body, but use "{ " and "}" enclose the statements participating in the loop.
　2. "Initialization", "Conditional Expression" and "Increment" in the for loop are all options, that is, they can be defaulted, but ";" cannot be defaulted. Initialization is omitted, which means no initial value is assigned to the loop control variable. If the conditional expression is omitted, it will become an infinite loop without other processing. If the increment is omitted, the loop control variable will not be operated. In this case, a statement to modify the loop control variable can be added to the statement body.
　3. The for loop can have multiple levels of nesting.
　Example:
　#include
　int main(void)
　{
　int i, j, k;
　printf("i j kn");
　for (i=0; i<2; i++) for (j=0; j<2; j++) for(k=0; k<2; k++)
　printf(%d %d %dn", i, j, k);
　 return 0;
　}
　 Output result For: i j k 0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1
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Enhance the for loop

　J2SE 1.5 provides another form of for loop with the help of. This form of for loop can traverse objects of types such as arrays and Collections in a simpler way. This article introduces the specific method of using this loop, explains how to define a class that can be traversed in this way, and explains the mechanism. Some common problems.
In a Java program, when you want to "process" - or "traverse" - the elements in an array or Collection, you usually use a for loop to achieve this (of course, use other It’s not impossible to use various types of loops, but I don’t know whether it’s because the length of the word for is relatively short, or because the meaning of the word for is more suitable for this kind of operation. In this case, the for loop is more commonly used than other loops.)
For traversing an array, the loop is generally written like this:
Listing 1: The traditional way of traversing an array
　/* Create an array*/
　int[] integers = {1, 2, 3, 4};
　/* Start Traversal*/
　for (int j = 0; j < integers.length; j++) {
　int i = integers[j];
　System.out.println(i);
　}
　For traversing Collection objects, this Loops usually take the form:
Listing 2: The traditional way of traversing Collection objects
　/* Create a Collection */
　String[] strings = {"A", "B", "C", "D"}
();
　System.out.println(str);
　}
　In the latest version of the Java language, J2SE 1.5, another form of for loop is introduced. With this form of for loop, you can now perform traversal work in a simpler way.
　 1. The second kind of for loop
Strictly speaking, the second kind of for loop in Java is basically in this format:
　 for (loop variable type loop variable name: object to be traversed) loop body
　 With the help of this syntax , the operation of traversing an array can be written like this:
Listing 3: A simple way to traverse an array
　/* Create an array*/
　int[] integers = {1, 2, 3, 4};
　/* Start Traverse */
　for (int i : integers) {
　System.out.println(i);/* Output "1", "2", "3", "4" in sequence */
　}
　 The for used here Loops will be viewed during compilation as this:
Listing 4: Equivalent code for a simple way to iterate through an array
　/* Create an array*/
　int[] integers = {1, 2, 3, 4} ;
　 /* Start traversing */
　 for (int variable name A = 0; variable name A < integers.length; variable name A ++) {
System.out.println (variable name A);/* Output "1", "2", "3", "4" in sequence */
　　}
　 The "variable name A" here is automatically generated by the compiler A name that won't cause confusion.
　The operation of traversing a Collection can also be written like this:
Listing 5: A simple way to traverse a Collection
　/* Create a Collection */
　String[] strings = {"A", "B", "C" , "D"};
　Collection list = java.util.Arrays.asList(strings);
　/* Start traversing*/
　for (Object str : list) {
　System.out.println(str);/* In sequence Output "A", "B", "C", "D" */
　}
　 The for loop used here will be viewed as this form during compilation: Listing 6: A simple way to traverse a Collection, etc. Price code/* Create a Collection */
　String[] strings = {"A", "B", "C", "D"};
　Collection stringList = java.util.Arrays.asList(strings);
　/ * Start traversing */
　for (Iterator variable name B = list.iterator(); variable name B.hasNext();) {
　System.out.println(variable name B.next());/* Output " A", "B", "C", "D" */
　}
　 The "variable name B" here is also a name automatically generated by the compiler that will not cause confusion.
　Because during compilation, the J2SE 1.5 compiler will regard this form of for loop as the corresponding traditional form, so there is no need to worry about performance problems.
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For loop in PHP

　　 //The FOR loop in PHP is basically consistent with the C language, as follows:
　for($i=1;$i<=100;$i++) {
　 Echo 'This is the '.$i.'th time';
　}
　 //Using the FOR loop, you can loop through a simple array
　 $array=Array('0'=>'a0','1'= >'b1','2'=>'c2','d'=>'d3');
　for($i=0;$i<=count($array);$i++){
echo $array[$i];
　}
　 //It should be noted that for arrays whose subscripts are not numbers, it is recommended to use the FOREACH loop to traverse the array.
　?>