Looping Programs using Java(part 1)

1) Print 1 1 1 1 1

This program prints number 1 five times.

public class Main {
    public static void main(String[] args) {
        for(int i = 1; i <= 5; i++) {
            System.out.print("1 ");
        }
    }
}

Output

1 1 1 1 1

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2) Print 1 2 3 4 5

public class Main {
    public static void main(String[] args) {
        for(int i = 1; i <= 5; i++) {
            System.out.print(i + " ");
        }
    }
}

Output

1 2 3 4 5

---

3) Print 1 3 5 7 9

Odd numbers can be printed by increasing by 2.

public class Main {
    public static void main(String[] args) {
        for(int i = 1; i <= 9; i += 2) {
            System.out.print(i + " ");
        }
    }
}

Output

1 3 5 7 9

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4) Print 3 6 9 12 15

Multiples of 3.

public class Main {
    public static void main(String[] args) {
        for(int i = 3; i <= 15; i += 3) {
            System.out.print(i + " ");
        }
    }
}

Output

3 6 9 12 15

---

5) Multiples of 3 and 5

Numbers divisible by both 3 and 5.

public class Main {
    public static void main(String[] args) {
        for(int i = 1; i <= 50; i++) {
            if(i % 3 == 0 && i % 5 == 0) {
                System.out.print(i + " ");
            }
        }
    }
}

---

6) Multiples of 3 or 5

Numbers divisible by either 3 or 5.

public class Main {
    public static void main(String[] args) {
        for(int i = 1; i <= 50; i++) {
            if(i % 3 == 0 || i % 5 == 0) {
                System.out.print(i + " ");
            }
        }
    }
}

---

7) Divisors of a Given Number

Example: divisors of 12 → 1 2 3 4 6 12

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int num = sc.nextInt();

        for(int i = 1; i <= num; i++) {
            if(num % i == 0) {
                System.out.print(i + " ");
            }
        }
    }
}

---

8) Count of Divisors

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int num = sc.nextInt();
        int count = 0;

        for(int i = 1; i <= num; i++) {
            if(num % i == 0) {
                count++;
            }
        }

        System.out.println("Count = " + count);
    }
}

---

9) Prime Number

A prime number has exactly 2 divisors.

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int num = sc.nextInt();
        int count = 0;

        for(int i = 1; i <= num; i++) {
            if(num % i == 0) {
                count++;
            }
        }

        if(count == 2)
            System.out.println("Prime");
        else
            System.out.println("Not Prime");
    }
}

---

10) Reverse Printing a Number

Example: 12345 → 5 4 3 2 1

public class Main {
    public static void main(String[] args) {
        int num = 12345;

        while(num > 0) {
            int digit = num % 10;
            System.out.print(digit + " ");
            num = num / 10;
        }
    }
}

---

11) Count of Digits

public class Main {
    public static void main(String[] args) {
        int num = 12345;
        int count = 0;

        while(num > 0) {
            count++;
            num = num / 10;
        }

        System.out.println(count);
    }
}

---

12) Sum of Digits

Example: 123 → 1+2+3 = 6

public class Main {
    public static void main(String[] args) {
        int num = 123;
        int sum = 0;

        while(num > 0) {
            sum += num % 10;
            num = num / 10;
        }

        System.out.println(sum);
    }
}

---

13) Reverse the Number

Example: 123 → 321

public class Main {
    public static void main(String[] args) {
        int num = 123;
        int rev = 0;

        while(num > 0) {
            rev = rev * 10 + num % 10;
            num = num / 10;
        }

        System.out.println(rev);
    }
}

---

14) Palindrome Number

A number is palindrome if reverse equals original.

Example: 121

public class Main {
    public static void main(String[] args) {
        int num = 121;
        int original = num;
        int rev = 0;

        while(num > 0) {
            rev = rev * 10 + num % 10;
            num = num / 10;
        }

        if(original == rev)
            System.out.println("Palindrome");
        else
            System.out.println("Not Palindrome");
    }
}

---

15) Armstrong Number

Example: 153

1³ + 5³ + 3³ = 153

public class Main {
    public static void main(String[] args) {
        int num = 153;
        int original = num;
        int sum = 0;

        while(num > 0) {
            int digit = num % 10;
            sum += digit * digit * digit;
            num = num / 10;
        }

        if(original == sum)
            System.out.println("Armstrong");
        else
            System.out.println("Not Armstrong");
    }
}

---

16) Neon Number

Example: 9

9² = 81

8 + 1 = 9

public class Main {
    public static void main(String[] args) {
        int num = 9;
        int square = num * num;
        int sum = 0;

        while(square > 0) {
            sum += square % 10;
            square = square / 10;
        }

        if(sum == num)
            System.out.println("Neon Number");
        else
            System.out.println("Not Neon Number");
    }
}

---

17) Strong Number

Example: 145

1! + 4! + 5! = 145

public class Main {
    public static void main(String[] args) {
        int num = 145;
        int original = num;
        int sum = 0;

        while(num > 0) {
            int digit = num % 10;
            int fact = 1;

            for(int i = 1; i <= digit; i++) {
                fact *= i;
            }

            sum += fact;
            num = num / 10;
        }

        if(sum == original)
            System.out.println("Strong Number");
        else
            System.out.println("Not Strong Number");
    }
}