Java puzzle 09: Demonstrating a for loop

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The process of loops is one of the most difficult concept for beginner programmers. To master loops you need to practice and parctice again. Therefore, I demonstrate many loops for beginners to solve. This loop is a for loop, which is often used in almost every Java program. You might need a pen and a paper if you can’t memorize the process. That is not necessary for advanced and intermediate programmers.

Java puzzle 9: Demonstrating a for loop

Level: Easy

What is the output of this program and why?

public class ForLoop
{
  public static void main(String[] args)
  {
    int x = 0;
    for(int i = 0; i < 5; i++)
    {
      x += i;
    }
    System.out.print(x);
  }
}
Author: Sar Maroof

Answer explanation

  1. The statement for(int i = 0; i < 5; i++) means repeat the process as long as the variable i is smaller than 5 starting with an initial value of i = 0. After each repetition the value of i is incremented by 1.
  2. According to the info of the step 1, the body of the loop is 5 times executed when i = 0, 1, 2, 3, 4 and after that the execution of the body of the loop is terminated.
  3. The initial value of the variable x is 0. So, the first time the initial value of x = x + i = 0 + 0 = 0.
  4. The second time the value of x becomes x = x + i = 0 + 1 = 1.
  5. The third time the value of x becomes x = x + i = 1 + 2 = 3.
  6. The fourth time the value of x becomes x = x + i = 3 + 3 = 6.
  7. The fifth time the value of x becomes x = x + i = 6 + 4 = 10.

The correct answer is x = 10 and the statement System.out.print(x); writes 10 to the standard output.





Sar Maroof is a professional software development teacher, gives master classes and publishes technical articles. He is also an expert software developer and worked for several big as well as small companies and later as a freelancer.

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