How to Use Substring in C#: Syntax and Examples

In C#, use the Substring method on a string to extract a part of it by specifying the start index and optionally the length. For example, myString.Substring(2, 4) returns 4 characters starting from index 2.

Syntax

The Substring method extracts a portion of a string starting at a specified index. It has two common forms:

• string.Substring(int startIndex): extracts from startIndex to the end of the string.
• string.Substring(int startIndex, int length): extracts length characters starting at startIndex.

Indexes start at 0, meaning the first character is at index 0.

csharp

string Substring(int startIndex);
string Substring(int startIndex, int length);

Example

This example shows how to extract parts of a string using both forms of Substring. It prints the extracted parts to the console.

csharp

using System;

class Program
{
    static void Main()
    {
        string text = "Hello, World!";

        // Extract from index 7 to end
        string part1 = text.Substring(7);

        // Extract 6 characters starting at index 7
        string part1Corrected = text.Substring(7, 6);

        // Extract 5 characters starting at index 0
        string part2 = text.Substring(0, 5);

        Console.WriteLine(part1); // Output: World!
        Console.WriteLine(part1Corrected); // Output: World!
        Console.WriteLine(part2); // Output: Hello
    }
}

Output

World!
World!
Hello

Common Pitfalls

Common mistakes when using Substring include:

• Using a startIndex that is negative or greater than the string length, which causes an ArgumentOutOfRangeException.
• Specifying a length that extends beyond the string's end, also causing an exception.
• Forgetting that string indexes start at 0, leading to off-by-one errors.

Always check string length before calling Substring to avoid errors.

csharp

string text = "Example";

// Wrong: startIndex too large
// string wrong = text.Substring(10); // Throws ArgumentOutOfRangeException

// Correct: check length first
if (text.Length > 3)
{
    string right = text.Substring(3);
    Console.WriteLine(right); // Output: mple
}

Output

mple

Quick Reference

Method	Description	Example
Substring(int startIndex)	Extracts substring from startIndex to end	"Hello".Substring(2) → "llo"
Substring(int startIndex, int length)	Extracts substring of length starting at startIndex	"Hello".Substring(1, 3) → "ell"

Key Takeaways

Use Substring(startIndex) to get part of a string from startIndex to the end.

Use Substring(startIndex, length) to get a specific length substring starting at startIndex.

String indexes start at 0; the first character is at index 0.

Avoid ArgumentOutOfRangeException by ensuring startIndex and length are within string bounds.

Always check string length before calling Substring to prevent errors.