Write a C program to calculate the shipping cost for an order based on the total weight of the items and the shipping method chosen by the customer. The store offers two shipping methods: standard and express. The shipping rates are as follows:

$$ Standard: $$2\mathrm{.}50$ per pound

$$ Express: $$5\mathrm{.}00$ per pound

However, there are certain conditions that affect the shipping cost:

$$ If the total weight of the items is above $10$ pounds, a discount of $10\%$ is applied to the shipping cost.

$$ If the shipping method chosen is express and the total weight is above $20$ pounds, an additional $$10$ discount is applied. Your program should prompt the user to enter the total weight of the items and the shipping method $(\text{'}$S$\text{'}$ for standard or $\text{'}$E$\text{'}$ for express$).$

Based on this input, the program should calculate and output the total shipping cost.