C# - Randomly Generating Strings

In C#, a string is a sequence of Unicode characters or an array of characters. The range of Unicode characters will be U+0000 to U+FFFF. A string is the representation of the text.   In this article, we will learn how to randomly generate strings and alphanumeric strings. So to do the task we use the Random class although it generates integers we can use them to create random strings. The Random class provides different types of methods to generate a random string. Random strings are generally used for captcha verification, etc.

Example:

Random String: ZDTXZFPYQEOUPGMEIYCEUSK

Random String: PSSR34YB

Method 1: Using Next() Method

We can generate a random string using the Next() method. This method takes two arguments minimum and maximum range and returns a positive random integer within the specified minimum and maximum range.

Syntax:

public virtual int Next (int mValue, int nValue);

Here, mValue is the upper boundary of the random number generated, and nValue is the lower bound of the random number returned.

Approach:

1. Create a object of the Random class

2. Randomly choose the size of the string using the Next() method and store in stringlength variable.

3. Repeat the following steps stringlength times using for loop:

• Randomly choose a number between 0 and 25
• Add 65 to the random number and convert it to char using convert.ToChar() method

4. Display the output.

Example:

// C# program to generate random strings
using System;

class GFG{

static void Main()
{

    // Creating object of random class
    Random rand = new Random();

    // Choosing the size of string
    // Using Next() string
    int stringlen = rand.Next(4, 10);
    int randValue;
    string str = "";
    char letter;
    for (int i = 0; i < stringlen; i++)
    {

        // Generating a random number.
        randValue = rand.Next(0, 26);

        // Generating random character by converting
        // the random number into character.
        letter = Convert.ToChar(randValue + 65);

        // Appending the letter to string.
        str = str + letter;
    }
    Console.Write("Random String:" + str);
}
}

Output:

Random String:UUYXBGA

Explanation: In the above example, we will generate a random number between 0 and 25 and add it to 65, then it will become the ASCII value of alphabets. The ASCII value is converted into character using the ToChar() method. This entire step will be repeated multiple times using for loop and a string is formed by appending all the randomly generated characters.

Method 2:

We can also generate random strings using this method. In this method, we pass a string that contains 26 alphabets. Then from the 26 alphabets, we will select a letter randomly and append it to the string, by repeating this a random string is formed.

Approach:

1. Initialize a string with alphabets i.e. str="abc.......xyz"
2. Initialize an empty string and name it as "ran".
3. Choose the size of the string to be generated.
4. Now using Next() method generate a random number and select the character at that index in the alphabet string.
5. Append that character to randomString.
6. Repeat steps 4 and 5 for n time where n is the length of the string.

Example:

// C# program to generate random strings
using System;

class GFG{

public static void Main(string[] args)
{
    Random res = new Random();

    // String of alphabets 
    String str = "abcdefghijklmnopqrstuvwxyz";
    int size = 10;

    // Initializing the empty string
    String ran = "";

    for (int i = 0; i < size; i++)
    {

        // Selecting a index randomly
        int x = res.Next(26);

        // Appending the character at the 
        // index to the random string.
        ran = ran + str[x];
    }

    Console.WriteLine("Random String:" + ran);
}
}

Output:

Random String:mphhzgvpjr

Explanation: In this example, we create an object of the Random class. Then we store 26 alphabets in a string named "str". Now we create a variable named "size" of integer type which represents the total number of characters present in the randomly generated string. Now we create an empty string named "ran". Then we create a for loop that iterates till "i  < size" and inside this for loop we use the Next() method. This method generates random numbers less than 26, so we use these numbers as a position indicator to get the character from that position. So every time when the loop iterate we will get a random character. And in the end, we will append these characters and get a random string.

Method 3: Generating alphanumeric string

Alphanumeric strings are those strings that contain both alphabets and numbers. We can generate random alphanumeric strings using the above method.

Approach:

1. Initialize a string with both alphabets and numbers i.e. str = "abc.......xyz012....789"
2. Initialize an empty string and name it as "randomString".
3. Choose the size of the string to be generated.
4. Now using Next() method generate a random number and select the character at that index in the alphanumeric string.
5. Append that character to randomString.
6. Repeat steps 4 and 5 for n time where n is the length of the string.

Example:

// C# program to generate random alphanumeric strings
using System;

class GFG{

public static void Main(string[] args)
{
    Random res = new Random();

    // String that contain both alphabets and numbers
    String str = "abcdefghijklmnopqrstuvwxyz0123456789";
    int size = 8;

    // Initializing the empty string
    String randomstring = "";

    for (int i = 0; i < size; i++)
    {

        // Selecting a index randomly
        int x = res.Next(str.Length);

        // Appending the character at the 
        // index to the random alphanumeric string.
        randomstring = randomstring + str[x];
    }

    Console.WriteLine("Random alphanumeric String:" + randomstring);
}
}

Output:

Random alphanumeric String:v91d2p48

Explanation: In this example, we create an object of the Random class. Then we store both alphabets and numbers in a string named "str". Now we create a variable named "size" of integer type which represents the total number of characters present in the randomly generated alphanumeric string. Now we create an empty string named "randomstring". Then we create a for loop that iterates till "i  < size" and inside this for loop we use the Next() method. This method generates random numbers less than str.Length, so we use these numbers as a position indicator to get the character from that position. So every time when the loop iterate we will get a random character. And in the end, we will append these characters and get a random alphanumeric string.