Deeply understand the logic control of C language

In this paper, the logic control of C language is discussed in depth. Generally speaking, the logic control statements of C language mainly include the following 7 types:

1. Goto is the most powerful, but is only used in special environments.
2, if the else
3, & # 63; :
4, the switch case
5, for
6, while
7, do the while

Since dijkstra's paper went To Statement Considered Harmful, the C code has rarely seen goto. (typically used for error handling of multiple resource allocations)
But from a computer's point of view, the lack of a goto (JMP) instruction really doesn't work. In fact, goto is the most consistent with our design flow chart.
Goto is also the most intuitive way to implement a flow chart. Goto can really get us where the heart goes, where the sword goes.

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

2, If statement

if ( conditions 1)
//Block 1
else
//Code block 2

Corresponding to goto:

t =  conditions 1 ; 
if (t Is true) goto true ; 
//Code block 2
goto finish
true : 
//Block 1
finish : 

3, The & # 63; : is equivalent to if else .

Only if statements are code blocks, okay? : is an expression.

 variable = ( conditions 1)?  expression 1 Expression: 2 ; 

Goto version:

t =  conditions 1 ; 
if (t To be true )
goto true ; 
//The variable is equal to expression 2
goto finish ; 
true : 
//The variable is equal to expression 1
finish : 

Note: The & # 63; : inside the expression as simple as possible, if too complex, use if statement to achieve, so convenient debugging.

4, The switch case

switch ( Conditional variable )
case  The element 1  : 
//Statement block 1;
break ; 
case  The element 2 : 
//Statement block 2;
break ; 
...
case  The element N
//Block N;
break ; 
default : 
//Default handling.
break ; 
}

Goto version:

 The jump table ={ The label 1 , the label 2 . ..., The label N }
goto  The jump table [ The element index]
//Label 1:
//Block 1
goto Finish
//Label 2:
//Block 2
goto Finish
...
//Label N:
//Block N
goto Finish
default : 
//Default handling.
Finish:

5, For statement

for ( Initialization statement; Judgment statement; Iteration statements )
//Loop block

Goto version:

//Initialization statement;
if ( Determine if the statement is no )
goto Finish ; 
loop : 
//Loop block
//Iteration statements
if ( Determine if the statement is true )
goto loop ; 
Finish : 

6, While statement

while( Condition is true )
//The code block
//Iterative block

Corresponding to goto version:

loop : 
t =  conditions 
if ( Is not true for ) goto Finish ; 
//The code block
//Iterative block
Finish : 

7, Do - while statement

do {
//Block 1
//Iterative block 1
} while ( Condition is true )

Goto version:

loop : 
//Block 1
//Iterative block 1
if ( Condition is true ) goto loop ; 

C language goto and assembly statement JMP series of instructions are logically identical.

Note:

1. There is a classical logical algebraic formula for the condition:
Morgan formula:
! (A && B) = (! (A) | |! B)
Suggest a table of algebraic operations for hand animation of complex logic
B A result
0 0 & # 63;
0 1 & # 63;
1 0 & # 63;
1 1 & # 63;
And ensure full coverage of unit tests.

2. Logical operations and bitwise operations are two groups that need to be distinguished.
With or against
Logic: && ||!
Bit: & | ~ ^

3. It is highly recommended to draw a complete flow chart on paper before writing code to comb your own design ideas.