while

Figure 161. A while loop Slide presentation 
final int repetitions = scan.nextInt(); ❶
int loopCount = 0; ❷

while (loopCount < repetitions ❸) {
   System.out.println("Do not copy!"); ❹
   loopCount++; ❺
}
Do not copy!
Do not copy!
Do not copy!
A while loop

❶

The code block will be repeated this number of times.

❷

Helper variable keeping track of repetitions.

❸

Condition to be checked prior each execution.

❹

Code block of statement(s) to be repeated.

❺

Helper variable being incremented during each iteration.


Figure 162. Combining increment and termination condition Slide presentation
Code Execution 
System.out.print("Enter repetitions: ");
final int repetitions = scan.nextInt();
int loopCounter = 0;

while (loopCounter++ < repetitions) {
   System.out.println("Do not copy!");
}
 
Enter repetitions: 3
Do not copy!
Do not copy!
Do not copy!

Figure 163. while syntax Slide presentation 
while (booleanExpression)
   (block | statement)

Figure 164. Empty while body Slide presentation 
int threeSeries = 1;

while ((threeSeries *=3 ) < 100);

System.out.println(threeSeries);

Exercise: Guess resulting output.


exercise No. 62

Generating square numbers

Q:

Write an application printing the first ten square numbers. The output should look like: 

The square of 1 is 1
The square of 2 is 4
The square of 3 is 9
The square of 4 is 16
The square of 5 is 25
The square of 6 is 36
The square of 7 is 49
The square of 8 is 64
The square of 9 is 81
The square of 10 is 100

A:

 
int counter = 0;

while (counter++ < 10) {
  System.out.println("The square of " + counter + " is " + counter * counter);
}

exercise No. 63

Calculating factorial

Q:

The factorial n ! of a given integer n is being defined as the following product:

n ! = n × ( n - 1 ) × ⋯ × 2 × 1

In addition the factorial of zero is being defined as:

0 ! = 1

Write an application asking a user for an integer value and calculate the corresponding factorial e.g.: 

Enter an integer value: 5
5! == 120

A:

 
public static void main(String[] args) {
  final Scanner scan = new Scanner(System.in);

  System.out.print("Enter an integer value: ");
  final int value = scan.nextInt();

  long factorial = 1;
  int i = 1;

  while (i++ < value) {
    factorial *= i;
  }

  System.out.println(value + "! == " + factorial);
}
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