While Loop with Number Series in Java

A while loop is useful for generating number series when the number of iterations is not known beforehand. Below are examples of different number series generated using a while loop.

1. Print Numbers from 1 to N 

int i = 1;
int n = 10;
while (i <= n) {
    System.out.print(i + " ");
    i++;
}

Output:

1 2 3 4 5 6 7 8 9 10

2. Print Even Numbers up to N 

int i = 2;
int n = 20;
while (i <= n) {
    System.out.print(i + " ");
    i += 2;  // Increment by 2 for even numbers
}

Output:

2 4 6 8 10 12 14 16 18 20

3. Print Odd Numbers up to N 

int i = 1;
int n = 20;
while (i <= n) {
    System.out.print(i + " ");
    i += 2;  // Increment by 2 for odd numbers
}

Output:

1 3 5 7 9 11 13 15 17 19

4. Print Fibonacci Series (First N Terms) 

int n = 10;
int a = 0, b = 1;
int count = 2;  // First two terms already known

System.out.print(a + " " + b + " ");

while (count < n) {
    int c = a + b;
    System.out.print(c + " ");
    a = b;
    b = c;
    count++;
}

Output:

0 1 1 2 3 5 8 13 21 34

5. Print Squares of Numbers (1 to N) 

int i = 1;
int n = 5;
while (i <= n) {
    System.out.print((i * i) + " ");
    i++;
}

Output:

1 4 9 16 25

6. Print Reverse Counting (N to 1) 

int i = 10;
while (i >= 1) {
    System.out.print(i + " ");
    i--;
}

Output:

10 9 8 7 6 5 4 3 2 1

7. Print Geometric Series (1, 2, 4, 8, 16, ...) 

int i = 1;
int n = 10;
while (i <= 100) {  // Stops when i exceeds 100
    System.out.print(i + " ");
    i *= 2;  // Multiply by 2 each time
}

Output:

1 2 4 8 16 32 64

8. Print Sum of Digits of a Number 

int num = 1234;
int sum = 0;
while (num > 0) {
    sum += num % 10;  // Extract last digit
    num /= 10;        // Remove last digit
}
System.out.println("Sum of digits: " + sum);

Output:

Sum of digits: 10 (1 + 2 + 3 + 4)

Key Takeaways

  • A while loop runs as long as the condition is true.
  • Useful when the number of iterations is not fixed.
  • Can generate number series, reverse counting, Fibonacci, etc.
  • Always ensure the loop has a termination condition to avoid infinite loops.

Would you like more examples or a quiz to test your understanding? 😊