documentation_english.txt

Computer Science Fundamentals Assignment Documentation
Created by: Hajnalka Horváth
Neptun code: XXNVW8
Date: 2022.10.01.-2022.11.30.
Input file: input.txt
Output file: output.txt

Task: Develop a program capable of performing basic arithmetic operations on integers stored in BCD format.

Operations:
Addition
Subtraction
Multiplication
Division

Conditions:
The task allows the use of maximum 32-bit arithmetic with shifting.
Implement operations using only addition, subtraction, negation, and logical operations.
Read data character by character from the file; string operations are not allowed.
There should be no errors during the execution of operations.
The solution should contain appropriate documentation for the program.

Solution:

The program first reads the file character by character:
i, j = loop variables
number1 = original first number stored in a list
number2 = original second number stored in a list
sign = operator sign
exercise = complete operation including '\n' stored in a list

Function Declarations:

def decimaltobcd = Convert a linked list of single-digit decimal numbers to a linked list of BCD numbers
    number = decnumber = list of decimal numbers
    number_bcd = number in BCD (linked list)
    bcd = BCD code of a digit
    endofnumber = while the original number divided by two has a remainder not equal to 0, it's false
number1_bcd = first number in BCD
number2_bcd = second number in BCD

def bcdtodecimal = Convert a linked list of BCD to either a normal list or an integer
    bcdnumber = number to convert
    decimal = a decimal digit
    decimalnumber = complete decimal number

def dectoint = Convert an array of single-digit decimal numbers to an integer
    dec = original decimal digit
    pos = position
    intnumber = number in integer format

def inttohexadecimal = Convert an integer to a hexadecimal number
    integer = original number
    hexa = hexadecimal representation of the number

def addition = Add numbers (first checks for exceptional cases, then performs conventional addition)
    bcd1 = number to which we add
    bcd2 = number to be added
    sum = result
    partial_result = partial result
    bcdidx = digit index
    bitidx = bit index within BCD
    carry = carry bit

def correction = Correct addition results, fix invalid BCDs (add 6 to the result)
    res = result
    correct = corrected version
    corresult = in case there is a carry during correction and it needs to be added to the preceding element
    end = end of calculation

def subtraction = Subtraction (add the 9's complement of the number to be subtracted from the smaller number, then increase the value by the remaining carry)
    minuend = smaller number
    subtrahend = number to subtract
    difference = result
    swap = swap (if the smaller number is greater, swap the two numbers and perform the subtraction)
    compliment9 = 9's complement of the entire number to be subtracted
    originaldec = decimal value of the number to be subtracted
    complbcd = 9's complement in BCD
    subtractresult = difference without correction (correction: add the remaining carry to the beginning of the number)

def multiplication = Multiply (multiply the multiplicand by itself)
    multiplicand = number to be multiplied
    multiplier = multiplier
    intmultiplier = multiplier in integer
    product = product

def division = Divide (determine how many times the divisor can be subtracted from the dividend)
    dividend = dividend
    divisor = divisor
    quotient = quotient, original value is 0, changed based on whether the dividend is greater than the divisor

Helper Functions:
    fill with 0's = to facilitate calculation, identical decimal places go to the same index
    which is smaller = aids in subtraction and division

The program executes the function corresponding to the operator sign.
result = final result
decimalresult = final result in decimal format
hexaresult = final result in hexadecimal format