Write a complete C program that demonstrates the usage of character strings. The program should declare an empty character array of specific size, and then ask user to enter a string to be stored in the array using a scanf function. The program should finally display the string entered to the screen for checking if the characters are correctly stored or not. Develop a user-defined function executing the steps needed for prompting the user by a simple message like Enter a string: and for entering the string. Keep in mind that arrays are passed-by-reference! b) Improve the program written in part (a) by calculating the string length and displaying it to the screen. Develop a user-defined function for calculating the string length. Show the usage of this function in the program. c) Improve the program written in part (b) by making a copy of the string entered to another empty character array inside the main function. The resulting copied string shall be displayed to the screen for checking purpose! Develop a user-defined function doing the string copying process. Show the usage of this function in the program. d) [if time allows] Improve the program written in part (c) by letting the user to specify two strings to be concatenated into a third one. Try concatenation process inside the main function first! Develop a user-defined function doing the string concatenation process. Show the usage of this function in the program.