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Loops & Iterations

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Loops (Iteration Statements)

🎯 Core Concept

Loops are programming constructs that allow repeated execution of a block of code based on a condition or over a sequence. They are fundamental to automation and repetitive task handling.

🔄 Types of Loops

Entry-Controlled Loops

Loops where the condition is checked before executing the loop body.

For Loop

Used when the number of iterations is known in advance.

# Python
for i in range(5):
    print(f"Iteration {i}")

// Java
for (int i = 0; i < 5; i++) {
    System.out.println("Iteration " + i);
}

While Loop

Used when the number of iterations is unknown and depends on a condition.

# Python
count = 0
while count < 5:
    print(f"Count: {count}")
    count += 1

// Java
int count = 0;
while (count < 5) {
    System.out.println("Count: " + count);
    count++;
}

Exit-Controlled Loops

Loops where the condition is checked after executing the loop body.

Do-While Loop

Executes the loop body at least once before checking the condition.

// Java
int count = 0;
do {
    System.out.println("Count: " + count);
    count++;
} while (count < 5);

🎮 Loop Control Statements

Break Statement

Immediately exits the loop, skipping remaining iterations.

Continue Statement

Skips the current iteration and moves to the next one.

📚 Common Use Cases

1. Processing collections - Iterating over arrays, lists, or datasets
2. Input validation - Repeatedly prompting until valid input
3. Mathematical calculations - Series, factorial, summation
4. Game loops - Continuous game state updates
5. File processing - Reading records until end of file

⚡ Performance Considerations

• Choose the right loop type based on the use case
• Avoid infinite loops by ensuring proper termination conditions
• Minimize work inside loops for better performance
• Consider built-in functions for common operations (map, filter, reduce)

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This atomic content can be included in Python, Java, C++, and general programming tutorials.

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📚 Practice Problems

Repetition is what computers do best. These problems will help you master for, while, and do-while loops, as well as nested loops for patterns.

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1. Print 1 to N

Rating: Newbie | Difficulty: Easy Input a number N and print all numbers from 1 to N.

💡 Hint

Use a for loop starting from 1 to N.

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2. Even Numbers from 1 to N

Rating: Newbie | Difficulty: Easy Input N and print all even numbers between 1 and N.

💡 Hint

Use if (i % 2 == 0) inside the loop, or increment the loop by 2: for (int i = 2; i <= N; i += 2).

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3. Factorial of a Number

Rating: Beginner | Difficulty: Easy Input a number and calculate its factorial (n!). E.g., 5! = 5 * 4 * 3 * 2 * 1 = 120.

💡 Hint

Initialize fact = 1 and multiply it by loop counter i in each iteration.

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4. Multiplication Table

Rating: Beginner | Difficulty: Easy Input a number and print its multiplication table up to 10.

💡 Hint

print(num + " x " + i + " = " + (num * i)).

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5. Sum of Digits

Rating: Intermediate | Difficulty: Medium Input a number and calculate the sum of its digits. E.g., 123 -> 1 + 2 + 3 = 6.

💡 Hint

Use num % 10 to get the last digit and num / 10 to remove it in a while loop.

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6. Reverse a Number

Rating: Intermediate | Difficulty: Medium Input a number and print its reverse. E.g., 123 -> 321.

💡 Hint

reverse = (reverse * 10) + (num % 10).

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7. Palindrome Number

Rating: Intermediate | Difficulty: Medium Check if a number is a palindrome (reads the same forward and backward). E.g., 121 is a palindrome.

💡 Hint

Reverse the number and compare it with the original value.

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8. Fibonacci Series

Rating: Beginner | Difficulty: Easy Print the first N terms of the Fibonacci series: 0, 1, 1, 2, 3, 5, 8, 13...

💡 Hint

Start with a = 0, b = 1. In each step, next = a + b, then update a = b and b = next.

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9. Prime Number Checker

Rating: Intermediate | Difficulty: Medium Input a number and check if it is prime (divisible only by 1 and itself).

💡 Hint

Check divisibility from 2 up to √num. If any number divides it, it's not prime.

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10. Armstrong Number

Rating: Advanced | Difficulty: Medium Check if a number is an Armstrong number. (Sum of cubes of digits equals the number itself, e.g., 153 = 1³ + 5³ + 3³).

💡 Hint

Extract each digit, cube it, and add to a sum.

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11. GCD (Greatest Common Divisor)

Rating: Advanced | Difficulty: Medium Find the GCD of two numbers.

💡 Hint

Use the Euclidean algorithm or a loop from 1 to the smaller of the two numbers.

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12. Power of a Number

Rating: Beginner | Difficulty: Easy Input base and exponent. Calculate base^exponent without using built-in math functions.

💡 Hint

Run a loop exponent times and multiply base each time.

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13. Star Pattern (Right Triangle)

Rating: Intermediate | Difficulty: Medium Print the following pattern for N rows:

*
**
***
****

💡 Hint

Use nested loops. Outer loop for rows, inner loop for columns (j <= i).

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14. Number Pattern

Rating: Intermediate | Difficulty: Medium Print the following pattern:

1
12
123
1234

💡 Hint

Similar to star pattern, but print the inner loop counter j.

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15. Perfect Number

Rating: Pro | Difficulty: Medium Check if a number is a Perfect Number (sum of its proper divisors equals the number, e.g., 6 = 1 + 2 + 3).

💡 Hint

Loop from 1 to num/2 and add the divisors.

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