Programming Tutorials

while loop iterations in java

By: aathishankaran in Java Tutorials on 2007-02-01  

One of the most important characteristics of a computer is its ability to execute a series of instructions repeatedly. This cycle introduces the concept of loops, which allow the user great flexibility in controlling the number of times a specific task is to be repeated.

The while loop:

A segment of code that is executed repeatedly is called a loop. The loop concept is essential to good problem solving techniques. A few examples of repetitions are:

Adding the marks in three subjects for 150 students
Counting even numbers from a list of 2000 numbers

The following code accepts ten numbers, finds their sum and display result:

PROGRAM_ADD

{
	integer Counter;
	integer Sum;
	integer Number;
	Counter = 0;
	Sum =0;
	while (Counter <10)
	{
		accept Number;
		Sum =Sum + Number;
		Counter = Counter+1;
	}
	display Sum;
	display "Execution completed successfully";
}

How can Counter ever be equal to Counter+1? From an algebraic point of view, this makes no sense. But this is an assignment statement, not an algebraic statement. The same variable name Counter appears on both sides of the assignment operator. This means that each time the statement is executed, the old value (the one on the right)is incremented by 1. The result is stored in the same variable, the one that appears on the left of the assignment operator.

The general form of a while loop is as follows:

while(condition)
(
  statement1;
  statement2;
}

The loop operates in the following fashion:

The condition enclosed in parenthesis is evaluated, if the result is true, then the body of the loop is executed, then the condition is evaluated again, if it is again true, the body of the loop is executed again.

This process continues until the test condition becomes false. At hat point, the loop is terminated immediately, and program execution continues with the statement (if any) following the while loop, if there are no more statements, the program terminates. The condition specified in a while loop can be a compound condition using logical operators.

Consider the following program sequence:

TEST_PROGRAM

{
	integer Counter;
	Counter = 1;
	while (Counter<11)
	{
		display "This is line number";
		display Counter;
		Counter = Counter+1;
	}
}

The output of this program will be:

This is line number 1
This is line number 2
This is line number 3
This is line number 4
This is line number 5
This is line number 6
This is line number 7
This is line number 8
This is line number 9
This is line number 10