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This article mainly shows you "dos how to achieve process jump", the content is easy to understand, clear, hope to help you solve your doubts, the following let the editor lead you to study and learn "dos how to achieve process jump" this article.

If different situations need to perform different established operations, if it is still in accordance with the conventional implementation process, it is impossible to complete the task, at this time, it is necessary to introduce the concept of process jump and use the process jump statement goto. The meaning of process jump is to change the default execution order and force the jump to a specified location to execute a specific block.

Let's take a look at an example: suppose you need to determine whether the user typed An or B, the code can be written like this:

@ echo off

Set / p input= Please enter the letter An or B:

If "% input%" = = "A" goto A

If "% input%" = = "B" goto B

Pause

Exit

: A

Echo, the letter you entered is A.

Pause

Exit

: B

Echo, the letter you entered is B.

Pause

Exit

According to the general execution process, all the code will be executed line by line from top to bottom, and the result will show two lines: "the letter you entered is A" and "the letter you entered is B". Obviously, this does not meet our requirements; however, the actual result is: if the letter you enter is either An or B, the result will only show "the letter you entered is A" or "the letter you entered is B". In other words, the order in which the code is executed has changed, no longer line by line from top to bottom: when the letter An is entered, the first if statement is executed, which jumps to the tag segment: a, bypassing all lines of code between the first if statement and: A. When the letter B is entered, the first two if statements are executed, and when the second if statement is executed, it jumps to the tag segment: B, bypassing all lines of code between the second if statement and: B.

As you can see from the above example, for the goto statement to work, you also need the cooperation of tag segments such as An or: B. The so-called tag segment is a block of code that begins with a single colon on the first line, followed by a string of characters, the second line and all subsequent behavioral code statement lines. In this case, the colon on the first line is the label flag, and the string immediately following it is the label signature, both of which are called labels. The following part of the goto statement is the label signature, which indicates where to jump after the execution of the statement, and the label receives the jump instruction of the goto statement and guides the subsequent operation of the goto statement. Goto statements and tags echo each other and complement each other in the realization of process jump.

Here are some considerations for using the jump statement goto:

1. Goto statements and tags should echo each other. There should not be only goto statements without corresponding tag segments, otherwise, the program will not find the corresponding tag segments and exit directly; only tag segments without goto statements are allowed, but the process jump function cannot be realized. From the point of view of code simplification, if there is a tag segment without goto statements, the tag is redundant and can be simplified.

2. If there are multiple tag segments, you need to pay attention to whether you need to add an appropriate exit statement between the tag segments to stop the program from continuing to execute downwards, which is easy for many beginners to make mistakes and need to be cautious. Taking the above code as an example, if you remove the exit statement between: an and: B, after entering the letter A, the result will display both "the letter you entered is A" and "the letter you entered is B", while the reserved exit statement will only press any key to launch the batch program after displaying "the letter you entered is A", because the batch is executed line by line from top to bottom Even after you jump with the goto statement, the execution process remains in the new location until another process jump statement is encountered, and the execution does not automatically terminate between the two tag segments.

3. Label names can only use constants, not variables

4. If there is a tag segment with the same name, the tag segment at the top level will be executed, and whether the subsequent tag segment will be executed will be dealt with on a case-by-case basis.

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