Random Number, string, password In C#

Introduction

The Random class of .NET class library provides functionality to generate random numbers in C#.
The Random class constructors have two overloaded forms. It takes either no value or it takes a seed value.

Details

The Random class has three public methods - Next, NextBytes, and NextDouble. The Next method returns a random number, NextBytes returns an array of bytes filled with random numbers, and NextDouble returns a random number between 0.0 and 1.0.

The following code returns a random number.

int randomNum = random.Next();

The following code returns a random number less than 1000.

int randomNum = random.Next(1000);

Example

The following code returns a random number between the min and the max range.

// Generate a random number between two numbers 
public int RandomNumber(int min, int max) 
{ 
  Random random = new Random(); 
  return random.Next(min, max); 
}

You can even combine the two methods - RandomNumber and RandomString to generate a combination of random string and numbers.

// Generate a random string with a given size 
public string RandomString(int size, bool lowerCase) 
{ 
  StringBuilder builder = new StringBuilder(); 
  Random random = new Random(); 
  char ch; 
  for (int i = 0; i < size; i++) 
  { 
    ch = Convert.ToChar(Convert.ToInt32(Math.Floor(26 * random.NextDouble() + 65))); 
    builder.Append(ch); 
  } 
  if (lowerCase) 
    return builder.ToString().ToLower(); 
  return builder.ToString(); 
}

The following code generates a password of length 10 with first 4 letters lowercase, next 4 letters numbers, and last 2 letters as uppercase.

// Generate a random password 
public string RandomPassword() 
{ 
  StringBuilder builder = new StringBuilder(); 
  builder.Append(RandomString(4, true)); 
  builder.Append(RandomNumber(1000, 9999)); 
  builder.Append(RandomString(2, false)); 
  return builder.ToString(); 
}