[C language switch branch statement and loop statement]

Type conversion

 Only data of the same type can be operated , If the data of different types needs to be converted to the same type before calculation .
1. Automatic type conversion ：
         Conversion rules ：(1,2,3 For priority )
                 On the basis of not losing data , Some space can be sacrificed appropriately 
                1、 Less bytes to more bytes 
                        char int 
                2、 Signed to unsigned 
                3、 Integer to floating point 
                 Be careful ：char short  If you operate with different types of data , Will be promoted to int Participate in the operation after type 
2. Cast ：
        ( New type name ) data ;
         Data may be lost in this way , Careful use 

switch Switch branch statement

switch(n)    //n It can be a number 、 expression , The result of the operation must be an integer 
    {
        case val:        // If val==n, Then turn on the execution switch 
            ...          //val Must be constant 
            break;        // Turn off the actuator switch . end swicth
            // If each case After all add break, Formed a branch structure 
            //switch Cannot be used in continue            
            //case a ... b: Can represent [a,b], But only GNU The compiler supports this syntax , Not recommended 
        case val1:
            ...
        default:
           // If all case It didn't open , Then finally open default, And it can be finally opened in any position 
    }

for Loop statement

  Loop is a way to make code execute repeatedly , Achieve the effect you want .
for Circulation is a very flexible 、 Varied and dangerous ( Compared with other cycles ) The cycle of 
for A loop usually uses a variable to guide the execution of the loop , This variable is called a loop variable i
for([1];[2];[3])
{
    [4]
}
[1]、 Assign initial values to cyclic variables ,C99 The above criteria can define the cyclic variable here  -std=gnu99
[2]、 Determine whether the loop variable reaches the boundary , If it doesn't arrive , Into the loop 
[4]、 Code that is executed repeatedly , Become a circular body .
[3]、 Changing the value of a loop variable , Prevent dead cycle , Generally, cyclic variables are self added 、 Self reduction  

for Cycle through various expressions ：

for(;;)  // Dead cycle 
{

}

int i=0;
for(; i<10;i++)
{


}   

for(int i=0; ;i++)
{
    if(i>=10)
    {
        break;
    }
}

for(int i=0; i<10;)
{
    ...
    i++;
}

while Loop statement

while( expression )
{
    // The loop body 
}
 Execute loop body when expression is true , Judge the expression again after execution , And so on , Until the expression is false , End of cycle .
while The cycle is equivalent to for Reduced version of             for(; expression ;)
for Loop is specially responsible for solving the problem of clearly knowing the number of cycles 
while Cycle is specially responsible for solving the problem of uncertain cycle times 

do-while Loop statement

do{
    // The loop body 
}while( expression );// Expression is true cyclic continuation , False to end the loop 
 Execute the loop first , And then judge the cyclic condition , The loop body is executed at least once 
 Suitable for working first 、 Special circumstances of post inspection , For example, enter a password 、 Judging the content of the document 

A nested loop

Loop statements contain loop statements
The outer loop is executed once , Memory loop execution n Time