Key Concept: Repetition is the third fundamental type of program control structure, following sequence and selection. Repeating steps in programming is called a loop. This section of the course describes three Java loop control statements: while, for, and do-while. The statements to be repeated are called the loop body.

Example:

for (int i = 0; i < 10; i++) {
    // Code to execute.
}

In this example:
i = 0; is the initializer,
i < 10; is the condition, and
i++ is the iterator.

String str = "loops";
// Process each character in the string:
for (char c : str.toCharArray()) {
    // Code to execute
}

List<String> names = new ArrayList<>();
names.add("Alice");
names.add("Bob");
names.add("Charlie");

for (String name : names) {
    System.out.println(name);
}

String input = "java";
for (char c : input.toCharArray()) {
    System.out.print(Character.toUpperCase(c) + " ");
}
// Output: J A V A

public class MultiplicationTable {
    public static void main(String[] args) {
        // Display the table title
        System.out.println("\t\t\t\tMULTIPLICATION TABLE\n");

        // Display column headers
        for (int j = 1; j <= 9; j++)
            System.out.print("\t" + j);

        System.out.println("\n\t_\t_\t_\t_\t_\t_\t_\t_\t_");

        // Display row headers and products
        for (int i = 1; i <= 9; i++) {
            System.out.print(i + "   |");
            for (int j = 1; j <= 9; j++) {
                System.out.printf("\t" + i * j);
            }
            System.out.println();
        }
    }
}

Program Explanation: The program first displays the table title. The first for loop prints numbers 1 through 9 as column headers, followed by a line of underscores. The second, nested for loop uses variable i for the outer loop (rows) and j for the inner loop (columns). For each value of i, the inner loop displays the product i * j for j = 1, 2, 3, ..., 9.

Lab 1: FOR Loop - Displaying Counter Values

Objective: Ask the user to input a number (N). Create a simple for loop with N repetitions that displays the values of the loop counter.

Expected Output:

Please enter a number and press Enter
3
The result:
Counter is at: 1
Counter is at: 2
Counter is at: 3

Please enter a number and press Enter
1
The result:
Counter is at: 1

File Name: L7Lab1.java
Class Name: L7Lab1

Algorithm:

1. Create a new Java file named L7Lab1.java.
2. Import the Scanner class: import java.util.Scanner;
3. Define the class L7Lab1 with a main method.
4. Inside the main method, create a Scanner object for input.
5. Prompt the user with System.out.println("Please enter a number and press Enter");
6. Read the integer input and store it in a variable N.
7. Print "The result:".
8. Create a for loop: for(int counter = 1; counter <= N; counter++)
9. Inside the loop, print the counter value: System.out.println("Counter is at: " + counter);
10. Run the program (e.g., press F5 in your IDE).
11. Test with different input values.
12. Place the task description as a comment at the top of the file.
13. Upload the file to the learning management system.

Lab 2: FOR Loop - Compute Factorial

Objective: Write a program that calculates and displays the factorial of an entered integer.

Expected Output (Example):

Enter an integer: 5
5! is 120

File Name: L7Lab2.java
Class Name: L7Lab2

Algorithm:

1. Create a new Java file named L7Lab2.java.
2. Import the Scanner class: import java.util.Scanner;
3. Define the class L7Lab2 with a main method.
4. Inside main, create a Scanner object.
5. Prompt the user: System.out.print("Enter an integer: ");
6. Read the integer input into a variable n.
7. Initialize a variable product = 1 to accumulate the factorial.
8. Create a for loop: for (int i = n; i > 1; --i)
9. Inside the loop, multiply product by i: product *= i;
10. After the loop, print the result: System.out.println(n + "! is " + product);
11. Run and test the program.
12. Add the task description as a comment at the file's beginning.
13. Upload the file.

Lab 3: NESTED Loop - Prime Numbers

Objective: Create a nested for loop to find and display all prime numbers less than 100 (starting from 2).

Expected Output (Excerpt):

Prime numbers:
2 is prime
3 is prime
5 is prime
7 is prime
11 is prime
...
97 is prime

File Name: L7Lab3.java
Class Name: L7Lab3

Algorithm:

1. Create a new Java file named L7Lab3.java.
2. Define the class L7Lab3 with a main method.
3. Print the header: System.out.println("Prime numbers:");
4. Declare two integer variables, e.g., outer and inner.
5. Create an outer for loop: for (outer = 2; outer < 100; outer++)
6. Inside it, create an inner for loop: for (inner = 2; inner <= (outer / 2); inner++)
7. Inside the inner loop, check divisibility: if ((outer % inner) == 0) break;
8. After the inner loop, check if inner > (outer / inner). If true, outer is prime. Print it.
9. Run the program to see all primes under 100.
10. Add a comment with the task description.
11. Upload the file.

Task 1: Sequence with Step 3

To do: Output the sequence: -3 0 3 6 9 12 15 18 21 24. Use a for loop with an iterator step of 3.

Note: Use counter += 3 as the iterator.

Expected Output:

File Name: L7Task1.java

Task 2: Symmetrical Sequence

To do: Output the sequence: 1 2 3 4 ... 99 100 99 ... 3 2 1.

Note 1: Create two for loops: the first for 1 2 ... 100, the second for 99 ... 2 1 (using i--).

Expected Output (Excerpt):

File Name: L7Task2.java

Task 3: Count Positive and Negative Numbers

To do: 10 integers are entered. Output the count of positive and negative numbers among them.

Note: Use a for loop for input. Check each number inside the loop. Use two counters.

Expected Output (Example with random numbers):

File Name: L7Task3.java

Task 4: Sum of Random Numbers

To do: 10 integers are randomly generated. Output these numbers and their sum.

Note 1: Use a for loop and a variable sum.

Note 2: Use (int)(Math.random() * 10) to generate integers 0-9. Adapt for a range that includes negatives if required.

Expected Output (Example):

File Name: L7Task4.java

Task 5: Sum of Odd Sequence

To do: Calculate the sum of the sequence: 1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 + 19. Generate the numbers using a loop; do not enter them.

Note: Use a variable named sum.

Expected Output:

File Name: L7Task5.java

Task 6: Product of Random Real Numbers

To do: 10 real numbers are entered or randomly generated. Output the numbers and their product.

Note 1: Use a for loop and a variable product.

Note 2: Initialize product as a double (e.g., 1.0).

Note 3: For random generation, you can use Math.random() * 20 for a range like 0.0 to 20.0.

Expected Output (Example):

File Name: L7Task6.java

Task 7: For-each - Filter Digits from String

To do: Extract and output only the digits from a given string. Use a for-each loop.

Note: Use the Character.isDigit() method.

Expected Output:

File Name: L7Task7.java

Task 8: For-each - Count Vowels in a String (Russian)

To do: Count the number of vowel letters (а, е, и, о, у, ы, э, ю, я) in a given string (consider lowercase only).

Note: Use indexOf() to check if a character is in the vowel string.

Expected Output:

File Name: L7Task8.java

Task 9: Nested Loops - Power Function

To do: For every x in the range [2;8], find the value of z(x,y) = x^y. The variable y ranges from 2 to 5.

Note: Use nested for loops: outer for x, inner for y. Use Math.pow(x, y) or a manual calculation loop.

Expected Output (Excerpt):

z(x,y) = 2^2 = 4
z(x,y) = 2^3 = 8
z(x,y) = 2^4 = 16
z(x,y) = 2^5 = 32
z(x,y) = 3^2 = 9
z(x,y) = 3^3 = 27
z(x,y) = 3^4 = 81
z(x,y) = 3^5 = 243
...

File Name: L7Task9.java

Task 10: For-each - Append Character

To do: Ask the user to enter a text and then a character. Output each character of the text with the entered character appended to it. Use a for-each loop.

Expected Output:

Enter the text, please:
>> Hello world!
Enter a character to add, please:
>> &
H& e& l& l& o&  & w& o& r& l& d& !&

File Name: L7Task10.java

Task 11: Nested Loops - Number Pyramid

To do: Write nested loops that display the following output pattern.

Note: Display the upper and lower parts using separate nested loops.

Expected Output:

  0
  0  1
  0  1  2
  0  1  2  3
  0  1  2  3  4
  0  1  2  3  4  5
  0  1  2  3  4
  0  1  2  3
  0  1  2
  0  1
  0

File Name: L7Task11.java