CENG242 - pe1 - Solved

Programming Language Concepts

1             Problem Definition
In this programming exam, you will help your friends who work in the IT department of a bank by implementing some Haskell functions. Each function will correspond to an independent, small feature which is useful for their customers or themselves in some certain calculations.

1.1           General Specifications
•    The signatures of the functions, their explanations and specifications are given in the following section. Read them carefully.

•    Make sure that your implementations comply with the function signatures.

•    You may define helper function(s) as you needed.

•    Importing any modules is not allowed for this exam. All you need is already available in the standard Prelude module.

•    Whenever you need to output a Double value (included in a list or by itself). You MUST use the following function to round it to 2 decimal places:

getRounded :: Double -> Double getRounded x = read s :: Double where s = printf
"%.2f" x
This tricky implementation uses printf function from Text.Printf module. This import and the implementation itself is already included in the template file. You can use it directly, while outputting Double values. The whole purpose of using this function is the simplification of the output, which will be useful in both debugging and evaluation processes.

2             Functions
2.1           convertTL (15 points)
You will implement a function named convertTL which takes a Double value and a String representing the name of currency which the given money in Turkish Liras will be converted to. Here is the signature of this function:

convertTL :: Double -> String -> Double
The abbreviations as representing Strings and the exchange rates [1] for the currencies are given in Table 1. No other currency will be tested.

Currency
Abbreviation
Exchange Rate
US Dollar
“USD”
8.18
Euro
“EUR”
9.62
Bitcoin
“BTC”
473497.31
Table 1: Exchange Rates with TL for Currencies
The function must convert the money in TL to the given currency using the proper exchange rate and return it as a Double.

SAMPLE I/O:

*PE1> convertTL 8180 "USD"

1000.0

*PE1> convertTL 12500 "EUR"

1299.38

*PE1> convertTL 1500000 "BTC"

3.17
2.2           countOnWatch (15 points)
As someone must monitor the servers of the bank at each night, some schedule is arranged for your friends. Your task is to implement a function named countOnWatch which takes a list of Strings as the schedule of the turns, a String representing the name of a certain employee and an Int representing the some number of days. This function shall calculate the number of watches assigned to this employee up to given days according to the arranged schedule. The function must return the calculated number as an Int.

Here is the signature of this function:

countOnWatch :: [String] -> String -> Int -> Int
SAMPLE I/O:

*PE1> countOnWatch ["Ali", "Huseyin", "Ahmet", "Derya", "Ali", "Fatma",

"Ali", "Ahmet"] "Ahmet" 5

1

*PE1> countOnWatch ["Ali", "Huseyin", "Ahmet", "Derya", "Ali", "Fatma",

"Ali", "Ahmet"] "Ali" 5

2

*PE1> countOnWatch ["Ali", "Huseyin", "Ahmet", "Derya", "Ali", "Fatma",

"Ali", "Ahmet"] "Ali" 8 3
2.3           encrypt (35 points)
You will implement a function named encrypt which takes an Int with 4 digits as the password of the customer and returns an Int as the encrypted password by processing the digits in the original one.

Here is the signature of this function:

encrypt :: Int -> Int
We will assume that the customers are not allowed to use a zero in any place for their password. Here are the rules to encrypt the rest of the digits:

•    If the digit is divisible by 3, you will subtract 1 from the digit.

•    If the digit is divisible by 4, you will multiply the digit by 2.

•    If the digit is divisible by 5, you will add 3 to the digit.

•    For the rest of the cases, you will add 4 to the digit.

•    If any of the above operation results in a double digit number, you will take the number in the ones place (e.g. 6 for 16.).

SAMPLE I/O:

*PE1> encrypt 6475

5818

*PE1> encrypt 9812

8656

*PE1> encrypt 3597

2881
2.4           compoundInterests (35 points)
You will implement a function named compoundInterests which calculates the money the customers would have after the compound interests are applied according to their initial money and how many years they want to invest their money to the bank.

Rules for the calculation of the total money that each customer would get will be given below. Let’s look at the signature of this function first:

compoundInterests :: [(Double, Int)] -> [Double]
This function takes a list of (Double, Int) pairs as the money and number of years for the investment of each customer. The function returns a list of Double as the total money that each customer would have for their investment. We will assume that there will be always at least one customer, when this function is called.

As the bank has the policy to compound the money monthly, here is the formula for the calculation of total money with compound interest:

                                                                                                                                                                         (1)

where T is the total money, P is the initial money, R is the annual interest rate and N is the number of years. We will use Table 2 to calculate annual interest rate (R) for the given initial money (P).

 
Money ≥ 10000
Money < 10000
Years ≥ 2
11.5%
9.5%
Years < 2
10.5%
9.0%
Table 2: Annual Interest Rates
Let’s say that a customer initially has 15000 TL, and wants to keep their money for 1 year to get the interest. Then we must use the annual interest rate as 10.5%. Hence, the calculation is done as below:

                                                                                                                                                                      (2)

By rounding the result to 2 decimal places, we get 16653.05 as the total money that customer would have after 1 year.

SAMPLE I/O:

*PE1> compoundInterests [(15000, 1)]

[16653.05]

*PE1> compoundInterests [(17557.5, 2), (9800, 1)]

[22073.68,10719.31]

*PE1> compoundInterests [(1575.25, 3), (12500, 1), (100000, 2)]

[2092.36,13877.54,125722.25]