How to Iterate Over Dictionary in C# - Simple Guide

In C#, you can iterate over a dictionary using a foreach loop on its KeyValuePair<TKey, TValue> elements. This lets you access both the key and value inside the loop easily.

Syntax

Use a foreach loop to go through each KeyValuePair<TKey, TValue> in the dictionary. Inside the loop, you can access the Key and Value properties.

• dictionary: your dictionary variable
• var pair: each key-value pair in the dictionary
• pair.Key: the key of the current item
• pair.Value: the value of the current item

csharp

foreach (var pair in dictionary)
{
    Console.WriteLine($"Key: {pair.Key}, Value: {pair.Value}");
}

Example

This example creates a dictionary of fruits and their colors, then iterates over it to print each fruit and its color.

csharp

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        var fruits = new Dictionary<string, string>
        {
            {"Apple", "Red"},
            {"Banana", "Yellow"},
            {"Grape", "Purple"}
        };

        foreach (var pair in fruits)
        {
            Console.WriteLine($"Fruit: {pair.Key}, Color: {pair.Value}");
        }
    }
}

Output

Fruit: Apple, Color: Red
Fruit: Banana, Color: Yellow
Fruit: Grape, Color: Purple

Common Pitfalls

One common mistake is trying to modify the dictionary (add or remove items) while iterating, which causes an error. Also, using foreach on just dictionary.Keys or dictionary.Values only gives keys or values, not both.

Always use KeyValuePair<TKey, TValue> to access both key and value together.

csharp

var dict = new Dictionary<int, string> { {1, "One"}, {2, "Two"} };

// Wrong: modifying dictionary during iteration
// foreach (var pair in dict)
// {
//     dict.Remove(pair.Key); // Throws InvalidOperationException
// }

// Correct way: collect keys first, then remove
var keys = new List<int>(dict.Keys);
foreach (var key in keys)
{
    dict.Remove(key);
}

Quick Reference

Here is a quick summary of how to iterate over a dictionary in C#:

Action	Code Example
Iterate keys and values	foreach (var pair in dictionary) { var key = pair.Key; var value = pair.Value; }
Iterate keys only	foreach (var key in dictionary.Keys) { }
Iterate values only	foreach (var value in dictionary.Values) { }
Avoid modifying during iteration	Collect keys first, then modify outside loop

Key Takeaways

Use foreach with KeyValuePair to access both keys and values in a dictionary.

Do not modify the dictionary while iterating over it to avoid runtime errors.

You can iterate keys or values separately using dictionary.Keys or dictionary.Values.

Collect keys first if you need to remove items during iteration.