C++ full subtractor using hexadecimals - c++

Question

I have input such as:
10000000000000-1=
and
AAAAABBBBBCCCCCDDDDDEEEEEFFFFF-ABCDEF0123456789ABCDEF=
I need to convert the hexadecimal strings digit by digit into decimal and keep track if I need to borrow. I'm not sure how to adjust the value of operand 1 when a borrow occurs. Such as in the first line when you have to borrow 13 times.
Currently, I have
#include <iostream>
#include <fstream>
using namespace std;
string decimalToHex(int);
void subtraction(string, string)
int hexadecimalToDecimal(char hexVal);
int fullSubtractor(int tempOp1, int tempOp2)
int main()
{
ifstream myFile;
string l1, l2, l3, l4, l5, l6, l7, l8; //lines
string l1op1, l1op2, l2op1, l2op2, l3op1, l3op2, l4op1, l4op2, l5op1, l5op2, l6op1, l6op2, l7op1, l7op2, l8op1, l8op2; //parsed operators
myFile.open("data.txt");
if (myFile.is_open()) //check if file opened
{
cout << "File opened successfully. " << endl;
}
else
{
cerr << "File failed to open." << endl;
return 1;
}
while (!myFile.eof())
{
myFile >> l6 >> l7; //read in line by line
}
l6op1 = l6.substr(0, l6.find("-"));
l6op2 = l6.substr(l6.find("-") + 1);
l6op2 = l6op2.substr(0, l6op2.length() - 1);
std::string l6op2_zeros = std::string((l6op1.length()) - l6op2.length(), '0') + l6op2;
cout << l6; // << subtraction(l6op1, l6op2_zeros) << endl;
subtraction(l6op1, l6op2_zeros);
cout << endl;
l7op1 = l7.substr(0, l7.find("-"));
l7op2 = l7.substr(l7.find("-") + 1);
l7op2 = l7op2.substr(0, l7op2.length() - 1);
std::string l7op2_zeros = std::string((l7op1.length()) - l7op2.length(), '0') + l7op2; //appends zeros to front of second operand to make it same length as operand 1
cout << l7; // << subtraction(l7op1, l7op2) << endl;
subtraction(l7op1, l7op2_zeros);
cout << endl;
myFile.close();
return 0;
}
int fullSubtractor(int tempOp1, int tempOp2)
{
static int borrow;
int result = 0;
if ((tempOp1 < tempOp2) || ((tempOp1 == 0) && (borrow == 1)))
{
tempOp1 += 16;
result = tempOp1 - borrow - tempOp2;
borrow = 1;
}
else
{
result = tempOp1 - tempOp2;
borrow = 0;
}
return result;
}
void subtraction(string op1, string op2)
{
string result;
int tempDifference = 0, tempHex = 0;
int j = op2.length() - 1;
for (int i = op1.length() - 1; i >= 0; i--)
{
int temp1 = hexadecimalToDecimal(op1[i]);
int temp2 = hexadecimalToDecimal(op2[j]);
tempHex = fullSubtractor(temp1, temp2);
result = decimalToHex(tempHex) + result;
cout << result << " ";
j--;
}
cout << result << endl;
//return result;
}
int hexadecimalToDecimal(char hexVal)
{
int base = 1;
int dec_val = 0;
if (hexVal >= '0' && hexVal <= '9')
{
dec_val += (hexVal - 48) * base;
base *= 16;
}
else if (hexVal >= 'A' && hexVal <= 'F')
{
dec_val += (hexVal - 55) * base;
// incrementing base by power
base *= 16;
}
return dec_val;
}
string decimalToHex(int decNum)
{
stringstream ss;
ss << hex << decNum;
string hexNum(ss.str());
//cout << hexNum << endl;
return hexNum;
}