Write a function called replace_at_index that takes three arguments - a string, an integer (representing an index), and a string. Return a string that is the same as the first string, except with the character at the specified index replaced by the second string.

Ask the user for some text, which index to replace, and what to replace that index with (in that order!).

Print out the result of calling your function.

The program in csharp is given below.

using System;

class Test

{

   //variables required to hold the strings and index

    static string line;

    static string test;

    static int idx;

    static string final="";

    static string replace_at_index(string str, int index, string s)

    {

        //replacement string inserted at the required position

        final = line.Insert(idx, test);

        //extra characters removed

        final = final.Remove(idx+test.Length, test.Length);

        return final;

    }

    static void Main()

    {

        Console.WriteLine("Enter a sentence");

        line = Console.ReadLine();

        Console.WriteLine("Enter the index to replace the string");

        idx = Convert.ToInt32(Console.ReadLine());

        Console.WriteLine("Enter the replacement string");

        test = Console.ReadLine();

        //the resultant string displayed

        Console.WriteLine("The string after replacement is "+ replace_at_index(line, idx, test));

    }    

}

OUTPUT

Enter a sentence

i am working now.

Enter the index to replace the string

3

Enter the replacement string

not

The string after replacement is i anotorking now.

Explanation:

1. Declare the variables to hold the user inputted strings, the index and the resultant string.

2. The variables are declared outside Main() and hence declared as static.

3. Inside Main(), user input is taken for the original string, the index to be replaced and the new replacement string.

4. Define the method, replace_at_index() that takes all the three user entered values as parameters and return the resultant string.

5. Inside replace_at_index() method, the replacement string is inserted into the original string at the required position using insert() method.

6. The resultant string is stored in the variable, final.

7. After insert(), remove() method removes the original character(s) which got shifted after the insert() operation.

8. The replace_at_index() method returns the resultant string having the replaced string inserted in the original string.

9. The whole code is written inside class as csharp is purely object-oriented language.

10. No object of any class is created since only a single class is involved.

11. The string operations have been done using the in-built string functions of csharp language.

12. The index of the string begins with 0 hence the string operations work accordingly.

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