Java puzzle 22: The do-while iteration

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This quiz shows that the do block is executed first then the condition is evaluated. That is what happens by the do-while loop and it is different with the while-loop and the for-loop.

Java puzzle 22: The do-while iteration

Level: Normal

What is the output of this program and why?

public class MyClass
{
  public static void main(String[] args)
  {
    int x = 1;
    int y = 3;
    do
    {
      x++;
      y += 2;
    }
    while(x + y < 12);
    System.out.print(x + "" + y);
  }
}

Author: Sar Maroof

Answer explanation

By do-while the do block is exectued before the evaluation of the condition. Therefore the statements x ++; and y += 2; increment the values of x and y by 1 and 2 respectively. So, x = 1 + 1 = 2. and y = 3 + 2 = 5.
The conditoon x + y < 12 returns true, because x + y = 2 + 5. Therefore the body of the loop is executed.
The statements x ++; and y += 2; increment the values of x and y by 1 and 2 respectively. So, x = 2 + 1 = 3; and y = 5 + 2 = 7. So, x + y = 10 and that is smaller less than 12.
The statements x ++; and y += 2; increment the values of x and y by 1 and 2 respectively. So, x = 3 + 1 = 4; and y = 7 + 2 = 9. So, x + y = 4 + 9 = 13 and that is greater than 12. Therefore the loop is terminated.
The code writes 49 to the standard output.

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Sar Maroof is graduated from HBO Amsterdam "higher professional education". He is a professional computer programming teacher, gives master classes and publishes technical articles. His experience with developing software started from 2001 and he has worked as a software developer for several big as well as small companies and later as a freelancer. He is the author of Java quizmaster and Build a Java application in 7 days.