In-depth understanding of C language-06-Logical Control

There are seven main types of Logic Control in C language:

1> goto is the most powerful, but it is generally used only in special environments.

2> if else

3>? :

4> switch case

5>

6> while

7> do while

Since dijkstra's article Go To Statement Considered Harmful, the C language code rarely sees goto. (It is generally used for troubleshooting multiple resource allocations)

However, from a computer perspective, the lack of a goto (jmp command) really cannot work. In fact, goto is the most consistent with our design flowchart.

It is also intuitive to use goto to implement a flowchart. Goto can truly let us do what our hearts are, and what the sword is.

Next, we will consider converting 2-7 to the corresponding goto language version (equivalent to converting to the corresponding assembly version ).

2 if statement

If (condition 1)

Code Block 1

Else

Code Block 2

Corresponding to goto:

T = condition 1;

If (t true) goto true;

Code Block 2

Goto finish

True:

Code Block 1

Finish:

3? : Is equivalent to if else.

Except that the if statement is a code block ,? : Is an expression.

Variable = (condition 1 )? Expression 1: expression 2;

Goto version:

T = condition 1;

If (t is true)

Goto true;

Variable = expression 2

Goto finish;

True:

Variable = expression 1

Finish:

Note :? : The expressions in it should be as simple as possible. if the expressions are too complex, use the if statement to implement the expressions, which facilitates debugging.

4 switch-case

Switch (Conditional Variable)

Case element 1:

Statement Block 1;

Break;

Case element 2:

Statement Block 2;

Break;

...

Case element N

Statement Block N;

Break;

Default:

Processing by default.

Break;

}

Goto version:

Jump table = {tag 1, tag 2,..., tag N}

Goto jump to the table [element index]

Label 1:

Statement Block 1

Goto Finish

Label 2:

Statement Block 2

Goto Finish

...

Tag N:

Statement Block N

Goto Finish

Default:

Processing by default.

Finish:

5>

For (initialization statement; judgment statement; iteration Statement)

Loop statement Block

Goto version:

Initialization statement;

If (whether the statement is "no)

Goto Finish;

Loop:

Loop statement Block

Iteration statement

If (statement true)

Goto loop;

Finish:

6> while

While (the condition is true)

Code block

Iteration Block

Corresponding goto version:

Loop:

T = Condition

If (not true) goto Finish;

Code block

Iteration Block

Finish:

7> do-while

Do {

Statement Block 1

Iteration Block 1

} While (the condition is true)

Goto version:

Loop:

Statement Block 1

Iteration Block 1

If (condition true) goto loop;

The goto in C language is logically consistent with the jmp command series in Assembly statements.

Note:

1> there is a classical Logical Algebra formula for the condition:

Morgan formula:

! (A & B) = (! A) | (! B)

We recommend that you manually draw an algebra two-dimensional table for complex logic.

Result of A B

0 0?

0 1?

1 0?

1 1?

It also ensures full coverage of the standalone test.

2> logical operations and bit operations are divided into two groups.

And

Logic: & |!

Bit: & | ~ ^ (Exclusive or)

3. We strongly recommend that you draw a complete flowchart on the paper and sort out your own design ideas before writing code.