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mohamed Tayel
mohamed Tayel

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Mastering List Enumeration in C#: Full Code Examples

When working with collections in C#, enumeration and manipulation of lists are fundamental skills. This article will cover key concepts: displaying ordered data, enumerating backward, and systematically removing elements, with complete code examples.

1. Displaying the Order When Enumerating

Displaying the position of each element in an ordered list is a common requirement. However, C# uses zero-based indexing, which can be confusing for users. Here's how to adjust for 1-based indexing.

Code Example 

using System; using System.Collections.Generic; class Program { static void Main() { List<string> countries = new List<string> { "China", "India", "USA", "Indonesia", "Pakistan", "Brazil", "Nigeria", "Bangladesh", "Russia", "Mexico" }; Console.WriteLine("Countries in Order:"); for (int i = 0; i < countries.Count; i++) { Console.WriteLine($"{i + 1}: {countries[i]}"); // 1-based index } } }
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Output 

Countries in Order: 1: China 2: India 3: USA 4: Indonesia 5: Pakistan 6: Brazil 7: Nigeria 8: Bangladesh 9: Russia 10: Mexico
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2. Enumerating Backwards

Sometimes, you need to iterate through a list in reverse order. This requires starting at the last index and decrementing.

Code Example 

using System; using System.Collections.Generic; class Program { static void Main() { List<string> countries = new List<string> { "China", "India", "USA", "Indonesia", "Pakistan", "Brazil", "Nigeria", "Bangladesh", "Russia", "Mexico" }; Console.WriteLine("\nCountries in Reverse Order:"); for (int i = countries.Count - 1; i >= 0; i--) { int displayIndex = countries.Count - i; // Adjusted for display Console.WriteLine($"{displayIndex}: {countries[i]}"); } } }
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Output 

Countries in Reverse Order: 1: Mexico 2: Russia 3: Bangladesh 4: Nigeria 5: Brazil 6: Pakistan 7: Indonesia 8: USA 9: India 10: China
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3. Systematically Removing Elements from a List

Removing items from a list during iteration can be tricky because indexes shift. One solution is to iterate backward.

Code Example 

using System; using System.Collections.Generic; class Program { static void Main() { List<string> countries = new List<string> { "China", "India", "USA", "Indonesia", "Pakistan", "Brazil", "Nigeria", "Bangladesh", "Russia", "Mexico" }; Console.WriteLine("\nRemoving countries with names shorter than 5 characters:"); for (int i = countries.Count - 1; i >= 0; i--) // Iterate backward { if (countries[i].Length < 5) { Console.WriteLine($"Removing: {countries[i]}"); countries.RemoveAt(i); } } Console.WriteLine("\nRemaining Countries:"); foreach (var country in countries) { Console.WriteLine(country); } } }
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Output 

Removing countries with names shorter than 5 characters: Removing: USA Removing: India Removing: China Remaining Countries: Indonesia Pakistan Brazil Nigeria Bangladesh Russia Mexico
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4. Combining Operations: Displaying and Filtering

You can combine enumeration with filtering. For example, display countries longer than five characters in reverse order.

Code Example 

using System; using System.Collections.Generic; class Program { static void Main() { List<string> countries = new List<string> { "China", "India", "USA", "Indonesia", "Pakistan", "Brazil", "Nigeria", "Bangladesh", "Russia", "Mexico" }; Console.WriteLine("\nFiltered and Reversed List:"); for (int i = countries.Count - 1; i >= 0; i--) { if (countries[i].Length > 5) { int displayIndex = countries.Count - i; Console.WriteLine($"{displayIndex}: {countries[i]}"); } } } }
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Output 

Filtered and Reversed List: 1: Mexico 2: Russia 3: Bangladesh 4: Nigeria 5: Pakistan 6: Indonesia
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Key Takeaways

  1. Control with for loops: Use the loop index to manage display order and modify it for user-friendly 1-based indexing.
  2. Iterate backward safely: When removing elements, reverse iteration prevents skipped or missed items.
  3. Flexibility with loops: Combine operations like filtering, enumeration, and ordering for custom requirements.

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