Why Does My Random String Generator Produce Identical Strings, and How Can I Fix It?

Random String Generator Consistency Issue

Problem Statement:

A random string generator is exhibiting unexpected behavior, producing identical four-character strings upon multiple invocations. The desired functionality is to generate two distinct random strings.

Code Snippet:

private string RandomString(int size)
{
    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);
    }

    return builder.ToString();
}

Resolution:

The inconsistency arises from creating a new instance of the Random class within the RandomString method. This results in the same seed value being used for each invocation, generating identical sequences.

Solution:

To ensure true randomness, move the instantiation of the Random class to a static field:

private static Random random = new Random((int)DateTime.Now.Ticks);

This ensures that a single instance of the random number generator is utilized throughout the program's lifetime. The DateTime.Now.Ticks value serves as a unique seed, guaranteeing that each subsequent call to RandomString produces a unique random string.

Modified Code:

private static Random random = new Random((int)DateTime.Now.Ticks);
private string RandomString(int size)
{
    StringBuilder builder = new StringBuilder();
    char ch;
    for (int i = 0; i < size; i++)
    {
        ch = Convert.ToChar(Convert.ToInt32(Math.Floor(26 * random.NextDouble() + 65)));                 
        builder.Append(ch);
    }

    return builder.ToString();
}

By implementing this change, the generator will now produce two distinct random strings:

// get 1st random string 
string Rand1 = RandomString(4);

// get 2nd random string 
string Rand2 = RandomString(4);

// creat full rand string
string docNum = Rand1 + "-" + Rand2;

Output:

UNTE-FWNU

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