How do I generate a random number in C# within a specific range?

General Discussions
, ,
1

I’m trying to generate a C# random number and want to make sure I do it correctly. I need an integer between two values, say between 1 and 100.

What’s the right way to create a random number generator in C# and use it to get values within a given range? A quick example would be helpful!

2

The most straightforward way is using Random.Next(min, max), which returns an integer from min (inclusive) to max (exclusive). So if you want a number between 1 and 100 including 100:

var rnd = new Random();
int number = rnd.Next(1, 101); // Upper bound is exclusive

Just be careful if you’re calling this repeatedly or in a tight loop. It’s best to create the Random instance once and reuse it. Creating new instances quickly can lead to the same number being generated because of time-based seeding.

3

If you’re working in a multithreaded app (like a web API), Random might not be thread-safe and could produce weird results under load.

That’s where System.Security.Cryptography.RandomNumberGenerator (or the newer RandomNumberGenerator.GetInt32) really shines:

using System.Security.Cryptography;

int number = RandomNumberGenerator.GetInt32(1, 101);

This not only avoids threading issues but also provides cryptographic-grade randomness, which is overkill for basic games but perfect if you’re doing anything security-related or concurrent.