Standard C language summary 2

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

                    //case a ... b Can be said [a,b], But only GNU The compiler supports this syntax , Not recommended

        break;     // Turn off the actuator switch , end switch,

                    // If each case all break, Formed a branch structure

                    //switch Cannot be used in continue coordination

        default：   // If all case It didn't open , Then finally open default,

                    // And it can be finally opened in any position

    }

for Loop statement

for([1];[2];[3])

    {

        [4]

    }

    [1]、 Assign initial values to cyclic variables , But only 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 , It is called circulatory body

    [3]、 Change the loop variables , Prevent dead cycle , Generally, cyclic variables are self added 、 Self reduction    

    1、2、4、3、2、4、3 ...

for(;;)          // Dead cycle usage

Brace question ：

        1、 It is recommended to align up and down

        2、 If there is only one line of code in the loop body , Braces can be omitted but are not conducive to expansion

            General business codes require that braces should not be omitted

while Loop statement

    while( expression )

    {

        // The loop body

    }

do while Loop statement

    do{

        // The loop body

    }while( expression );// The expression continues with a true loop , False to end the loop

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 first

    recompute

    Automatic type conversion ：

        Conversion rules ： On the basis of not losing data , Some space can be sacrificed appropriately

                1、 Less bytes to more bytes

                2、 Signed to unsigned

                3、 Integer to floating point

                Be careful ： char short When calculating with different types of data ,

                Will be promoted to int Participate in the operation after type

        Cast ：

            ( New type name ) data ;

            Data may be lost in this way , Careful use