LESSON 122 OF 409 · WHILE LOOPS & FOR LOOPS

For Loops: Printing Numbers II in C++ (Time Complexity: O(n))

Let's see an example where we change the iteration statement.

We can print all even numbers from 2 through 10:

for (int i = 2; i <= 10; i += 2) {
	cout << i << endl;
}

The output of this code is:

Let's break down this code:

The initialization statement is int i = 2, so we start iterating from number 2.
The condition statement is i <= 10 so we end at number 10. We could've written i < 11 and it would still be correct.
The iteration statement is i += 2, so we increase our number by 2 every time.

Assignment

Let's print all odd numbers from 7 through 23 using a for loop.

Hint
Look at the examples above if you get stuck.

STEP 1 OF 2

Guided

Ctrl + Enter to check

Printing Numbers 4 in C++, explained

Understanding the Problem

The core challenge of this problem is to correctly set up a for loop that iterates through a specific range of numbers and prints only the odd numbers. This is a common task in programming that helps in understanding loop constructs and iteration control.

Significance: This problem is fundamental in learning how to control loops and is widely applicable in scenarios where specific conditions need to be met during iteration.

Potential pitfalls include incorrect initialization, condition, or iteration statements that could lead to infinite loops or incorrect outputs.

Approach

To solve this problem, we need to:

Initialize the loop variable to the first odd number in the range, which is 7.
Set the loop condition to ensure the variable does not exceed 23.
Increment the loop variable by 2 in each iteration to ensure only odd numbers are printed.

Naive Solution

A naive solution might involve checking each number in the range to see if it is odd, but this is not optimal as it involves unnecessary checks.

Optimized Solution

The optimized solution directly iterates through the odd numbers by starting at 7 and incrementing by 2 each time:

for (int i = 7; i <= 23; i += 2) {
    cout << i << endl;
}

Algorithm

Step-by-step breakdown:

Initialize the loop variable i to 7.
Set the loop condition to i <= 23.
In each iteration, print the value of i.
Increment i by 2.
Repeat until the condition is no longer met.

Code Implementation

#include <iostream>
using namespace std;

int main() {
    // Loop from 7 to 23, incrementing by 2 each time
    for (int i = 7; i <= 23; i += 2) {
        // Print the current value of i
        cout << i << endl;
    }
    return 0;
}

Complexity Analysis

The time complexity of this approach is O(n), where n is the number of iterations. In this case, n is the number of odd numbers between 7 and 23, which is a constant. The space complexity is O(1) as we are using a fixed amount of extra space.

Edge Cases

Potential edge cases include:

If the range does not include any odd numbers (not applicable here as 7 and 23 are both odd).
If the range is very large, but the approach remains efficient due to the constant step size.

Testing

To test the solution comprehensively:

Check the output for the given range (7 to 23).
Test with different ranges to ensure the loop correctly handles various start and end points.
Use a mix of small and large ranges to verify performance.

Thinking and Problem-Solving Tips

When approaching such problems:

Clearly define the range and the step size.
Ensure the loop conditions are correctly set to avoid infinite loops.
Practice with different loop constructs to understand their behavior.

Conclusion

Understanding how to control loops and iterate through specific ranges is crucial in programming. This problem helps in grasping these concepts and applying them effectively.

Encourage readers to practice similar problems to strengthen their understanding and problem-solving skills.

Additional Resources

For further reading and practice:

Keep going with C++About 340 step-by-step lessons, from your first line of code to coding interviews. Free to start.

Start learning free