Why is the GOTO statement re-used in C #?

Source: Internet
Author: User
Tags case statement
For goto statements, it is no longer recommended in C/C ++, and there is no goto in Java. Why does the GOTO statement be re-used in C?

First, let's take a look at the usage of the GOTO statement in C:
1) The basic function is to execute the statement in the place where the user jumps to the label as before.

// Exp1 valid Code
{

{

Goto labela;

}
Labela:

}

2) but in C #, Goto can only jump out of one statement block, or jump to another place in one statement block;
3) It is not allowed for a goto to jump out of a block into a block. // Exp2.1 valid Code
// Goto jump in the same statement Block
{

{

Goto labela;


Labela:

}


}


// Exp2.2 Invalid code
// Goto jump from the block to the block [Error]
{

{

Goto labela; // error. cannot jump into a statement Block

{

Labela:

}
}


}

4) A valid statement must be followed after the label corresponding to goto, that is, the label cannot be placed at the end of a statement block. // Exp3 Invalid code
{

{

Goto labela;

}

Labela: // error: labela should follow a valid statement.
}

The above is the basic usage of the GOTO statement, and the only useful part of goto in C # is to use it in conjunction with the switch statement. In other places, remember that the GOTO statement is not recommended.
Let's take a look at the syntax of the switch statement: www. elivn. comswitch (expression)
{
Case 1:
.. // (1) Error Syntax: No break statement is added to jump out
Case 2:
..
Break;
Case 3: // (2) Correct syntax: No break statement exists.
Case 4:
.
Break;
Default:
.
Break;
}
// Compare the two cases above without the break statement at the end,
// However, It is correct and incorrect. We can see that (1) the case is followed by a statement, and (2) it is not followed by any statement.
// In this way, we can know that in C #, the use of (1) is not allowed, and the use of (2) is allowed.
// That is to say, if the previous case statement is not followed by any valid statement, it will automatically jump into the next case,
// However, if the previous case statement is followed by any valid statement, you cannot directly jump into the following case.
// ▲Here the GOTO statement is needed to jump into the next case.

Switch (expression)
{
Case 1:
..
Goto case 2; // (1) Correct syntax
Case 2:
..
Break;
Case 3: // (2) Correct syntax: No break statement exists.
Case 4:
.
Break;
Default:
.
Break;
}

// Actually, The Goto here also acts as a break,
// Here, the switch statement of C # does not allow traversing between case and case. You can only use the GOTO statement to implement this function.
// As to the definition, it should be the programming habits of some masters of Ms.
// Ps. C # allows the flow control of the switch part that contains 0 statements to continue (traverse) The next switch part.

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