Implement this using C language

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 **               Telephone Directory Maintenance System
 **                           Specification
 **               (Programming Fundamentals Project)
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 **Author - Sudhir S B
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 *Question Details
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 *Login screen
        • User Id for login should be your employee id
        • If your employee id is entered for User ID, Main Menu of Telephone Directory Maintenance System should be displayed
        • If any other employee id is entered for User Id, the system should display error message "Login Denied” and should quit the application
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 *Add Department
        • The department code should be 4 characters long
        • The department names should not exceed 15 characters
        • The department code should start with 1000. Every new department added should get a 1 up number for the department code
        • The department codes should be unique
        • Department names cannot be duplicated. Comparison should be case insensitive
        • The department codes should be generated by the system
        • When the user finishes adding new departments, the control should return to the Department Code Maintenance Screen 
View all Departments
        • Display all the departments along with the department codes in a tabular format  
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 *Add New Employee
        • All fields are mandatory.
        • The name of the Employee should not exceed 25 characters.
        • The employee id should be 4 characters long.
        • The employee id should start with 1000. Every new employee added should get a 1 up number for the employee id
        • The employee ids should be unique
        • The employee ids should be generated by the system
        • When the control comes to accepting the department code, list the existing department codes along with their names on the screen for selection of the proper department code
        • Department Code must be a valid code (should be existing in dept.txt file)
        • Department name is displayed corresponding to the code entered. User should not edit this field
        • The Location should not exceed 5 characters
        • When the user finishes adding new Employee, the control should return to the
        Employee Maintenance Screen
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 *View all Employees
        • Display all the employees along with their department codes, employee id and other details in a tabular format
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 *Add New Telephone
        • All fields are mandatory
        • The employee id entered should exist
        • If the employee id does not exist, an error message should be displayed
        • The Location and Department Code (for the employee) should be displayed (From the information entered in the Employee Master screen). User should not edit these fields
        • Allocate a seven-digit telephone number depending on the department. (4-digit Department Code + 3-digit unique number starting with 001 for a particular department). The first telephone number in a particular department should start with xxxx001
        • The telephone number should be generated by the system and should be sequential
        • When the user finishes adding new Telephone Number, the control should return to the Telephone Directory Maintenance Screen
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 *Enquiry on Employee Name
        • Case insensitive name search should be provided
        • If the name does not exist, an error message should be displayed
        • If the name exists, the details of all the telephone numbers whose owner names match should be displayed
        • When the user finishes inquiry by employee, the control should return to the
        Telephone Enquiry Screen
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 *Enquiry on Telephone Number
        • Telephone number should exist.
        • If the telephone number does not exist, an error message should be displayed
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