C++ for Loop Code Explanations

Explore solved C++ while loop exercises, including a multiplication table, algorithm analysis, dry run, complete code, code explanation, and sample output.

Contents

• Example 7: Nested for Loops – Printing a Rectangle Pattern

Example 7: Nested for Loops – Printing a Rectangle Pattern

1. Problem Analysis

Problem: Write a C++ program using nested for loops to print a rectangular pattern of stars (*).

Requirements:

• Print 4 rows.
• Print 5 stars in each row.
• Use an outer for loop to control the rows.
• Use an inner for loop to print the stars in each row.
• Move to the next line after printing all 5 stars in a row.

Understanding the problem:

Think of the output as a rectangle:

• The outer loop runs 4 times (4 rows).
• The inner loop runs 5 times for each row (5 stars).
• cout << endl; moves the cursor to the next line after each row.

2. Algorithm

1. Start the program.
2. Initialize the outer loop variable i = 1.
3. Repeat the outer loop while i <= 4.
4. Inside the outer loop:
   • Initialize the inner loop variable j = 1.
   • Repeat the inner loop while j <= 5.
   • Print * during each iteration.
   • Increment j by 1.
5. After the inner loop finishes, move to the next line using endl.
6. Increment i by 1.
7. Repeat until the outer loop finishes.
8. End the program.

3. Pseudocode

START

FOR i = 1 TO 4

    FOR j = 1 TO 5
        PRINT "* "
    END FOR

    PRINT NEW LINE

END FOR

STOP

4. Dry Run Table

The outer loop controls the rows, while the inner loop controls the stars printed in each row.

Total iterations:

• Outer loop: 4 iterations.
• Inner loop: 5 iterations per outer loop iteration.
• Total stars: 4 × 5 = 20 stars.

5. Complete C++ Code

#include <iostream>
using namespace std;

int main()
{
    for (int i = 1; i <= 4; i++)
    {
        for (int j = 1; j <= 5; j++)
        {
            cout << "* ";
        }

        cout << endl;
    }

    return 0;
}

6. Detailed Code Explanation (Line by Line)

Line 1: Include the input/output library

#include <iostream>

• Includes the input/output stream library.
• Allows us to use cout to display output on the screen.

Line 2: Use the standard namespace

using namespace std;

• Allows us to use standard C++ objects such as cout and endl without writing std:: before them.

Line 3: Main function

int main()

• The main() function is the starting point of the program.
• Program execution begins from this function.
• int indicates that the function returns an integer value.

Line 4: Opening curly brace

{

• Marks the beginning of the main() function body.

Line 5: Outer for loop

for (int i = 1; i <= 4; i++)

This loop controls the number of rows.

It contains three parts:

How it works:

• First iteration: i = 1 (Row 1).
• Second iteration: i = 2 (Row 2).
• Third iteration: i = 3 (Row 3).
• Fourth iteration: i = 4 (Row 4).

The outer loop executes 4 times, so the program prints 4 rows.

Line 6: Opening curly brace of the outer loop

{

• Marks the beginning of the outer loop body.
• The statements inside these braces execute during each iteration of the outer loop.

Line 7: Inner for loop

for (int j = 1; j <= 5; j++)

This loop controls the number of stars in each row.

It also contains three parts:

How it works:

• First iteration: j = 1 (First star).
• Second iteration: j = 2 (Second star).
• Third iteration: j = 3 (Third star).
• Fourth iteration: j = 4 (Fourth star).
• Fifth iteration: j = 5 (Fifth star).

The inner loop executes 5 times for every iteration of the outer loop.

Line 8: Print the star

cout << "* ";

• Displays a star (*) on the screen.
• The space after the star separates it from the next star.
• This statement executes 5 times during each row.

Line 9: Closing curly brace of the inner loop

}

• Marks the end of the inner loop.
• After printing 5 stars, the inner loop terminates.

Line 10: Move to the next line

cout << endl;

• Moves the cursor to the next line.
• Executes after the inner loop finishes.
• Ensures that each new row starts on a separate line.

Line 11: Closing curly brace of the outer loop

}

• Marks the end of the outer loop.
• The outer loop increments i and starts the next row.
• This process continues until 4 rows have been printed.

Line 12: Return statement

return 0;

• Terminates the main() function.
• Returns 0 to indicate successful program execution.

Line 13: Closing curly brace

}

• Marks the end of the main() function.

7. Sample Output

* * * * *
* * * * *
* * * * *
* * * * *

8. Important Concepts to Remember

Remember this simple rule:

• Outer loop = Rows.
• Inner loop = Columns (stars).
• endl = Move to the next row.