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

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.
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.
The initial value of the variable x is 0. So, the first time the initial value of x = x + i = 0 + 0 = 0.
The second time the value of x becomes x = x + i = 0 + 1 = 1.
The third time the value of x becomes x = x + i = 1 + 2 = 3.
The fourth time the value of x becomes x = x + i = 3 + 3 = 6.
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.