On the usage details and special usage of switch case

About switch-case Of Basic usage Everyone must have known something about it , I won't go over it here . Let's go straight to the point , Talk about using switch-case Some of Little details .

Detail one

switch ( expression ）
{

    case  result 1：
         sentence 1;
        break;  

    case  result 2：
         sentence 2;
        break;

    ....

    default:
         sentence n;
        break;
}

For example, the above form , among switch after expression The value of must be An integer value （ for example ： integer , Character , Enumeration, etc ）, And the value must be the same as case The result type is the same ;case Can only be Constant or constant expression ;

...
int a=2,b=2;
switch (a)
{
    
    case b:
        printf("o");
    default :
        printf("s");
   
}

...

  The execution result is ： Compile error . because case After b It's a variable. , Even though he was assigned .

Detail two

...

switch (2)
{
    default :
        printf("s");
    
    case 1:
        printf("o");

}

...

In the above code , The running result is ：so

Because assembly code interpretation switch The way of statement is ： Judge first if there is case Matches , If not, you will arrive default To execute .

default It can be placed anywhere , But the execution order is always at the end of the branch .

Detail three

Please compare the three programs and distinguish their output

①

...

switch (2)
{
    default :
        printf("s");
        break;
    
    case 1:
        printf("o");
        break;
}

...

result ：s

②

...

switch (2)
{
    default :
        printf("s");
    
    case 1:
        printf("o");
        break;

}

...

result ：so

③

...

switch (2)
{
    default :
        printf("s");
        break;
    
    case 1:
        printf("o");

}

...

result ：s

The specific reason is as detailed in detail 2 ;

switch-case Special use of

case It can express the range

...
int a;
scanf("%d",&a);

switch (a)
{ 
    case 1 ... 10:
        printf("1\n");
        break;

    case 11 ... 20:
        printf("2\n");
        break;

    case 21 ... 30:
        printf("3\n");
        break;

    default:
        printf(" I don't know \n");
        break;
}

...

In the code snippet above , If input ：9, The output ：1< enter >;

                                     Input ：25, The output ：3< enter >;

                                     Input ：99, The output ： I don't know < enter >;

Be careful ：case Can only represent integer range after , In the symbol “...” There must be a space before and after ;

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