Hexadecimal Calculator for Addition and Subtraction

Question

I have an issue with my program which is used to calculate addition and subtraction for Hexadecimals. The algorithm of my program is:

• Take 2 strings inputted by the user, and "+" or "-" depending on the operator they chose
• Convert the 2 strings into decimals, and add or subtract
• If the second number is bigger, use the bigger number to subtract the smaller number, and put a "-" in front of it when returning the result (1 - 8 should = -7, but instead, I take 8 - 1 = 7, and return "-" and "7" so it gives "-7)
• Take the decimal result from the operation and convert back to hexadecimal
• Return string of hexadecimal

However, I have run into a issue where my calculations give me wrong answers. (For e.g FFFFFF + FFFFFFFFFF prints "FFFFFFE" instead of "10000FFFFFE")

What can I do to solve the issue?

I created my own Power function for this program as I need a a number that can go up to 16 Fs for the Hexadecimal string.

Power Function:

unsigned long long int result = 1;
int i;

for (i = 0; i < y; i++)
{
    result *= x;
}

return result;

Code:

int i;
int power = FirstHexaNumber.length() - 1;
int power2 = SeconHexaNumber.length() - 1;
int checkLength = FirstHexaNumber.length();
int checkLength2 = SeconHexaNumber.length();
unsigned long long int decimalNumber = 0;
unsigned long long int decimalNumber2 = 0;
unsigned long long int totalDecimal;
int temporary;
string result;

if (Operator == '+')                            //check if operator is add or minus
{
    //Convert Hex to Decimal for first number

    for (i = 0; i < checkLength; i++)
    {
        if (int(FirstHexaNumber[i]) >= 48 && int(FirstHexaNumber[i]) <= 57) {       // check if FirstHexaNumber 0 to 9

            decimalNumber += ((int(FirstHexaNumber[i])) - 48) * powerFunc(16, power);   //formula to convert hexadecimal into decimal, int(FirstHexaNumber[i]) is used to convert hexa into a number
        }
        else if (int(FirstHexaNumber[i]) >= 65 && int(FirstHexaNumber[i]) <= 70)    // check if FirstHexaNumber is A to F
        {
            decimalNumber += ((int(FirstHexaNumber[i])) - 55)*powerFunc(16, power);
        }
        else if (int(FirstHexaNumber[i]) >= 97 && int(FirstHexaNumber[i]) <= 102)   // check if FirstHexaNumber is a to f
        {
            int x = powerFunc(16, power);
            decimalNumber += ((int(FirstHexaNumber[i])) - 87)* x;
        }
        power--;            //power-- since it starts from "HexaNumber.length - 1". Power should decrease as assignment of power goes down
    }

    //Convert Hex to Decimal for second number

    for (i = 0; i < checkLength2; i++)
    {
        if (int(SeconHexaNumber[i]) >= 48 && int(SeconHexaNumber[i]) <= 57) {

            decimalNumber2 += ((int(SeconHexaNumber[i])) - 48) * powerFunc(16, power2);     //formula to convert Hexadecimal to Decimal
        }
        else if (int(SeconHexaNumber[i]) >= 65 && int(SeconHexaNumber[i]) <= 70)
        {
            decimalNumber2 += ((int(SeconHexaNumber[i])) - 55)*powerFunc(16, power2);       //formula to convert Hexadecimal to Decimal
        }
        else if (int(SeconHexaNumber[i]) >= 97 && int(SeconHexaNumber[i]) <= 102)
        {
            unsigned long long int x = powerFunc(16, power2);
            decimalNumber2 += ((int(SeconHexaNumber[i])) - 87)*x;       //formula to convert Hexadecimal to Decimal
        }
        power2--;
    }

    totalDecimal = decimalNumber + decimalNumber2;                                  //Adds the total decimal to convert into hexadecimal

    if (totalDecimal == 0)
    {
        return "0";
    }

    //Converts Decimal to Hexadecimal
    for (i = 0; totalDecimal != 0; i++)             //as long as totalDecimal does not hit 0 from being divided by 16, run the loop
    {
        temporary = totalDecimal % 16;              //use temporary as a variable to temporarily hold onto the number remainder of mod 16

        if (temporary >= 10)                        //if temporary >= 10, that means it needs to be converted to alphabet
        {
            result.insert(0, 1, temporary + 55);    //result.insert inserts a string of text into a spot, and pushes everything else backwards.
        }                                           //in this case, result.insert assigns "temporary+55" into the spot of characters 0 to 1.

        else                                        //else, it means that the decimal will be a number, add 48 to convert to ascii          
        {
            result.insert(0, 1, temporary + 48);
        }
        totalDecimal = totalDecimal / 16;           //divide by 16 to move on to finding the next digit/alphabet
    }

    return result;
}
else if (Operator == '-')                           //check if operator is add or minus
{
    //Convert Hex to Decimal for first number

    for (i = 0; i < checkLength; i++)               //as long as the loop does not exceed the length of the hexadecimal, run it
    {
        if (int(FirstHexaNumber[i]) >= 48 && int(FirstHexaNumber[i]) <= 57) {

            decimalNumber += ((int(FirstHexaNumber[i])) - 48) * powerFunc(16, power);
        }
        else if (int(FirstHexaNumber[i]) >= 65 && int(FirstHexaNumber[i]) <= 70)
        {
            decimalNumber += ((int(FirstHexaNumber[i])) - 55)*powerFunc(16, power);
        }
        else if (int(FirstHexaNumber[i]) >= 97 && int(FirstHexaNumber[i]) <= 102)
        {
            decimalNumber += ((int(FirstHexaNumber[i])) - 87)*powerFunc(16, power);
        }
        power--;    
    }

    //Convert Hex to Decimal for second number

    for (i = 0; i < checkLength2; i++)
    {
        if (int(SeconHexaNumber[i]) >= 48 && int(SeconHexaNumber[i]) <= 57) {

            decimalNumber2 += ((int(SeconHexaNumber[i])) - 48) * powerFunc(16, power2);
        }
        else if (int(SeconHexaNumber[i]) >= 65 && int(SeconHexaNumber[i]) <= 70)
        {
            decimalNumber2 += ((int(SeconHexaNumber[i])) - 55)*powerFunc(16, power2);
        }
        else if (int(SeconHexaNumber[i]) >= 97 && int(SeconHexaNumber[i]) <= 102)
        {
            decimalNumber2 += ((int(SeconHexaNumber[i])) - 87)*powerFunc(16, power2);
        }
        power2--;
    }

    if (decimalNumber >= decimalNumber2)
    {
        totalDecimal = decimalNumber - decimalNumber2;          //subtract bigger number by smaller number.

        if (totalDecimal == 0)
        {
            return "0";
        }

        for (i = 0; totalDecimal != 0; i++)
        {
            temporary = totalDecimal % 16;

            if (temporary >= 10)
            {
                result.insert(0, 1, temporary + 55);
            }
            else
            {
                result.insert(0, 1, temporary + 48);
            }
            totalDecimal = totalDecimal / 16;
        }

        return result;
    }
    else
    {
        totalDecimal = decimalNumber2 - decimalNumber;          //subtract bigger number by smaller number.

        if (totalDecimal == 0)
        {
            return "0";
        }

        for (i = 0; totalDecimal != 0; i++)
        {
            temporary = totalDecimal % 16;

            if (temporary >= 10)
            {
                result.insert(0, 1, temporary + 55);
            }
            else
            {
                result.insert(0, 1, temporary + 48);
            }
            totalDecimal = totalDecimal / 16;
        }

        return "-" + result;
    }

}
return 0;

Answer 1

You can try this snippet:

int a,b;
cout << "\nEnter A in hex: ";
cin >> hex >> a;
cout << "\nEnter B in hex: ";
cin >> hex >> b;
cout << "\n Addition of " << hex << a <<" and "<< hex << b << " is " << hex << a+b;
cout << "\n Substraction of " << hex << a << " and " << hex << b << " is " << hex << a - b;

Answer 2

int x = powerFunc(16, power); should be long long x = powerFunc(16, power); Don't know full source of the function pow, the return type should be long long too.

Hexadecimal Calculator can be more simple.

#include <sstream>
std::stringstream ss1(s1),ss2(s2);
ss1 >> std::hex >> i1;
ss2 >> std::hex >> s2;

std::cout << std::hex << std::uppercase << i1 + s2 << std::endl;

std::stringstream res;
res << std::hex << std::uppercase << i1 + i2;
return res.str();