Use switch Case statement as my roll no is odd

Program must be in C language not in C++

Please Must use USER DEFINE FUNCTION for calculating surcharge

Construct a program to calculate the electricity bill. The rates of electricity per unit are as follow: If the units consumed are equal or less than 100, then the cost is Rs. 2/- per unit. If the units consumed are more than 100 or less than equal to 200, then the cost is Rs. 2.5/- per unit. If the units consumed are more than 200 or less than equal to 300, then the cost is Rs. 3/- per unit. If the units consumed are more than 300, then the cost is Rs. 3.5/- per unit and surcharge of 5% of bill is added. (Use user-defined function for calculating surcharge). Implement the program by using switch case (for odd roll number students) and if-else ladder (for even roll number students)