$4.$a$)$ A store offers bulk purchase discounts based on the quantity of items purchased:

$1-10$ items: No discount

$11-50$ items: $5\%$ discount

$51-100$ items: $10\%$ discount

$$ More than $100$ items: $15\%$ discount

Design an algorithm to calculate the final price after applying the appropriate bulk purchase discount.

b$)$ A store offers different discounts based on the payment method:

$$ Cash: No additional discount

$$ Credit Card: $2\%$ additional discount

$$ Debit Card: $3\%$ additional discount

$$ Mobile Payment: $5\%$ additional discount

Create a C program that calculates the final price after applying the appropriate bulk purchase discount.

c$)$ A store offers discounts based on the total purchase amount as follows:

$$ Up to Rs$\mathrm{.}500,$ there is no discount.

$$ Between Rs$\mathrm{.}500$ and Rs$\mathrm{.}1000,$ a $5\%$ discount is applied.

$$ Between Rs$\mathrm{.}1000$ and Rs$\mathrm{.}2000,$ a $10\%$ discount is applied.

$$ Above Rs$\mathrm{.}2000,$ a $15\%$ discount is applied.

Create a C program to calculate the final price after applying the appropriate discount.

d$)$ Combine all previously mentioned discounts into one comprehensive program. The program should:

$$ Apply the base discount based on the total purchase amount.

$$ Apply the payment method discount.

$$ Apply the discount based on quantity.