The do-while loop

  • Syntax of the do-while-statement in Java: 

       do
       one-statement;  // Loop body
   while ( loop-contuation-condition )  ;   // must end with ; 

or:

   do
   { // Loop body
       statement1;
       statement2;
       ...
   } while ( loop-contuation-condition )  ;  // must end with ;

  • Effect of the do-while statement:

    1. Execute the loop body

    2. Check the loop-contuation-condition

    3. If true:   repeat
      If false, continue with the next statement in the program

The do-while loop    Flow chart 

     do
 { // Loop body
   statements(s);
 } while ( loop-contuation-condition )  ;

  • The flow chart of the do-while statement is:

The do-while loop    Example

  • Use a do-while loop:

      • Write a program that read a list of (positive) integer numbers until 0 and print their sum

  • Plan for the program: 

        sum = 0

  repeat:
  {
     x = read next number; 

     if ( x != SENTINEL )  // SENTINEL == 0
        sum = sum + x;

  } as long as: (x != SENTINEL)

The do-while loop    Example

  • Solution in Java: 

        Scanner input = new Scanner(System.in);
      
  int sum = 0;
  int x = -1;
      
  do
  {
     System.out.print("Enter an integer (ends if it is 0): ");
     x = input.nextInt();
         
     if ( x != 0 )
        sum = sum + x;
  } while ( x != 0 );
      
  System.out.print(sum);

DEMO: demo/05-loops/03-do-while/ReadAndSum.java

Comment

 

  • The do-while loop is rarely used by programmers

  • The most useful loop statements in any programming language are:

      • The while loop

      • The for loop that we will discuss next