Loop structure: while and do while structures

while loop

1. Grammatical structure

        Initial value ;

          switch( The loop condition ){

                Loop operation code ;

                Iteration part ;

          }

2. The law of execution ：

        1） First, execute the initial value code ;

         2） Judge cyclic condition , If the cycle condition is true, Is executed {} Loop operation code and iteration code in ,

                After iteration , Continue to return to judge the cycle condition , Decide whether to continue the loop operation according to the result of the loop judgment ; If the cycle condition is false, End the whole while Loop structure , Carry on while The code after the loop structure

3. Be careful ：

        1） The initial value code is executed only once ;

        2） No matter how simple or complex it is written , The result can only be Boolean , Either for true Either for false;

        3) The function of the iteration part is to change the initial value , Let the cycle condition no longer be satisfied at a certain time , To end the whole while  Loop structure .

         // Use while Cyclic output 100 Study hard and make progress every day 
		//  Initial value 
		int i = 1;
		while (i <= 100) {//  The loop condition  i<=100  The loop condition 
			System.out.println(" The first " + i + " All over ： study hard and make progress every day ");//  Cyclic operation 
			i++;//  iteration ： The purpose of iteration is to change the initial value , In order to be at a certain moment ,
			       // Let the cycle condition no longer be satisfied , End loop operation , If there is no iteration , The cycle goes into a dead cycle 

		}
		System.out.println(" The program is finished ");

do-while loop  

1. Grammatical structure

        Initial value

        do{

                Loop operation code ;

                Iteration part ;

       }while( The loop condition );

2. The law of execution ：

       1） First, execute the initial value code

        2） Get into {} Execute a loop operation code and iterate part of the code , Judge the condition after execution ,

                        If the condition is true, return {} Execute loop operation code and iteration part code in ,

                         If the condition is false, End the whole do-while Loop structure , So let's keep going do-while The code after the loop structure

3. Be careful ：

        1） The initial value is executed only once ;

        2） No matter how simple or complex it is written , The result can only be Boolean , Either for true Either for  false;

        3）do-while Loop is to execute a loop operation first , In judging cycle conditions , therefore , If the first judgment cycle condition is not satisfied , The loop operation will also be performed once （do-while The loop operation in the loop will be executed at least once ）

        //  Use do-while Cyclic output 1-100 Value 
		// initialization 
		int i=1;
		do{
			System.out.println(" value ："+i);// Cyclic operation 
			i++;// iteration 
		}while (i<=100);// The loop condition 	

while Circulation and do-while loop The difference between ：

1） Execution order is different ;

2） When the initial conditions are not met ：

        while A loop will not execute ;

        do-while The loop executes at least once in any case