How to Check if String Contains Substring in C#

In C#, you can check if a string contains a substring using the Contains method. It returns true if the substring is found and false otherwise. For example, myString.Contains("text") checks if "text" is inside myString.

Syntax

The Contains method is called on a string variable and takes another string as an argument. It returns a boolean value indicating if the substring exists inside the main string.

• string.Contains(substring): Checks if substring is part of string.
• Returns true if found, false if not.

csharp

bool result = mainString.Contains(substring);

Example

This example shows how to use Contains to check if one string is inside another and prints the result.

csharp

using System;

class Program
{
    static void Main()
    {
        string mainString = "Hello, welcome to C# programming!";
        string substring = "welcome";

        bool contains = mainString.Contains(substring);

        Console.WriteLine($"Does the main string contain '{substring}'? {contains}");
    }
}

Output

Does the main string contain 'welcome'? True

Common Pitfalls

One common mistake is ignoring case sensitivity. The Contains method is case-sensitive, so "Welcome" and "welcome" are different. To check without case sensitivity, convert both strings to the same case using ToLower() or ToUpper().

Another pitfall is passing null as the substring, which causes an exception.

csharp

string mainString = "Hello, welcome to C# programming!";
string substring = "Welcome";

// Case-sensitive check (will be false)
bool result1 = mainString.Contains(substring);

// Case-insensitive check (convert both to lower case)
bool result2 = mainString.ToLower().Contains(substring.ToLower());

Console.WriteLine(result1); // False
Console.WriteLine(result2); // True

Output

False
True

Quick Reference

Method	Description	Example
Contains	Checks if substring exists (case-sensitive)	str.Contains("text")
ToLower + Contains	Case-insensitive check	str.ToLower().Contains(sub.ToLower())
IndexOf	Returns position or -1 if not found	str.IndexOf("text") >= 0

Key Takeaways

Use Contains to check if a string includes a substring in C#.

Contains is case-sensitive; use ToLower() or ToUpper() for case-insensitive checks.

Passing null to Contains causes an error; always ensure substring is not null.

For position info, IndexOf can be used instead of Contains.