I’m stuck on this error. I’m wondering if I can get a second set of eyes.TIA

#include <iostream>
#include <iomanip>
#include <vector>
#include <string>
#include <limits>
#include <climits>

using namespace std;

class BigInt {
private:
    vector<char> v;

    BigInt fiboHelper(BigInt n, BigInt a = 0, BigInt b = 1) {
        if (n.size() == 0)
            return a;
        else if (n.size() == 1)
            return b;
        else
            return fiboHelper(n - 1, b, a + b);
    }
public:
    BigInt() {}

    BigInt(int num) {
        while (num > 0) {
            v.insert(v.begin(), num % 10);
            num /= 10;
        }
    }
    BigInt(string num) {
        for (char digit : num) {
            if (isdigit(digit))
                v.push_back(digit - '0');
        }
    }
    BigInt operator+(const BigInt& bigInt) const{
        BigInt result;
        int carry = 0;
        int i = v.size() - 1;
        int j = bigInt.v.size() - 1;

        while (i >= 0 || j >= 0 || carry) {
            int sum = carry;
            if (i >= 0) sum += v[i--];
            if (j >= 0) sum += bigInt.v[j--];

            result.v.insert(result.v.begin(), sum % 10);
            carry = sum / 10;
        }
        return result;
    }
    BigInt operator+(int num) {
        return *this + BigInt(num);
}

    BigInt operator-(BigInt other) {
        BigInt result;
        int borrow = 0;
        int i = v.size() - 1;
        int j = other.v.size() - 1;
        
        while (i >= 0 || j >= 0) {
            int diff = borrow;
            if (i >= 0) diff += v[i--];
            if (j >= 0) diff -= other.v[j--];

            if (diff < 0) {
                diff += 10;
                borrow = -1;
            } else {
                borrow = 0;
            }
            result.v.insert(result.v.begin(), diff % 10);
        }
        while (!result.v.empty() && result.v.front() == 0)
            result.v.erase(result.v.begin());
        return result;
    }
    bool operator>=(const BigInt& other) const {
        if (v.size() != other.v.size())
            return v.size() > other.v.size();
        
        for (int i = 0; i < v.size(); ++i) {
            if (v[i] != other.v[i])
                return v[i] > other.v[i];
        }
        return true;
    }
    bool operator==(const BigInt& other) const {
        if (v.size() != other.v.size())
            return false;

        for (int i = 0; i < v.size(); ++i) {
            if (v[i] != other.v[i])
                return false;
    }

    return true;
}
    BigInt operator*(BigInt other) {
        BigInt result;
        result.v.resize(v.size() + other.v.size(), 0);

        for (int i = v.size() - 1; i >= 0; --i) {
            int carry = 0;
            for (int j = other.v.size() - 1; j >= 0; --j) {
                int product = v[i] * other.v[j] + result.v[i + j + 1] + carry;
                result.v[i + j + 1] = product % 10;
                carry = product / 10;
            }
            result.v[i] += carry;
        }
        while (!result.v.empty() && result.v.front() == 0)
            result.v.erase(result.v.begin());

        return result;
    }
    BigInt operator/(BigInt other) {
        BigInt quotient;
        BigInt remainder = *this;
        BigInt divisor = other;
        BigInt divisorShifted;
        BigInt subtrahend;
        BigInt temp;
        while (remainder >= divisor) {
            int shift = remainder.size() - divisor.size();
            divisorShifted = divisor;
            divisorShifted = divisorShifted.shiftLeft(shift);
            temp = 1;
            temp = temp.shiftLeft(shift);
            while (remainder >= divisorShifted) {
                remainder = remainder - divisorShifted;
                quotient = quotient + temp;
            }
        }
        return quotient;
    }
    BigInt operator%(BigInt other) {
        BigInt quotient;
        BigInt remainder = *this;
        BigInt divisor = other;
        BigInt divisorShifted;
        BigInt subtrahend;
        BigInt temp;
        while (remainder >= divisor) {
            int shift = remainder.size() - divisor.size();
            divisorShifted = divisor;
            divisorShifted = divisorShifted.shiftLeft(shift);
            temp = 1;
            temp = temp.shiftLeft(shift);
            while (remainder >= divisorShifted) {
                remainder = remainder - divisorShifted;
                quotient = quotient + temp;
            }
        }
        return remainder;
    }
    BigInt operator++(int) {
        *this = *this + 1;
        return *this - 1;
    }
    BigInt operator++() {
        *this = *this + 1;
        return *this;
    }
    BigInt operator[](int index) {
        if (index >= 0 && index < v.size()) {
            return v[index];
        } else {
            return BigInt();
        }
    }
    void print() {
        for (char digit : v)
            cout << static_cast<int>(digit);
    }
    int size() {
        return v.size();
    }
    BigInt fibo() {
        return fiboHelper(*this);
    }
    bool operator>(const BigInt& other) const {
    if (v.size() != other.v.size())
        return v.size() > other.v.size();

    for (int i = 0; i < v.size(); ++i) {
        if (v[i] != other.v[i])
            return v[i] > other.v[i];
    }
    return false;
}
    BigInt fact() {
        BigInt result = 1;
        BigInt current = *this;
        while (current > 1) {
            result = result * current;
            current = current - 1;
        }
        return result;
    }
    friend ostream& operator<<(ostream& os, const BigInt& num) {
        if (num.v.size() <= 12) {
            for (char digit : num.v)
                os << static_cast<int>(digit);
        } else {
            os << fixed << setprecision(7) << num.toExponential();
        }
        return os;
    }
    BigInt shiftLeft(int n) const {
        BigInt result = *this;
        for (int i = 0; i < n; ++i)
            result.v.push_back(0);
        return result;
    }
private:
    string toExponential() const {
        string str;
        str.push_back(v[0] + '0');
        str.push_back('.');
        for (size_t i = 1; i < 7 && i < v.size(); ++i)
            str.push_back(v[i] + '0');
        str.push_back('e');
        str += to_string(v.size() - 1);
        return str;
    }
};
void testUnit()
{
    int space = 10;
    cout << "anTestUnit:n"<<flush;
    system("whoami");
    system("date");
    BigInt n1(25);
    BigInt s1("25");
    BigInt n2(1234);
    BigInt s2("1234");
    BigInt n3(n2);
    BigInt fibo(12345);
    BigInt fact(50);
    BigInt imax = INT_MAX;
    BigInt big("9223372036854775807");
    cout << "n1(int) :"<<setw(space)<<n1<<endl;
    cout << "s1(str) :"<<setw(space)<<s1<<endl;
    cout << "n2(int) :"<<setw(space)<<n2<<endl;
    cout << "s2(str) :"<<setw(space)<<s2<<endl;
    cout << "n3(n2) :"<<setw(space)<<n3<<endl;
    cout << "fibo(12345):"<<setw(space)<<fibo<<endl;
    cout << "fact(50) :"<<setw(space)<<fact<<endl;
    cout << "imax :"<<setw(space)<<imax<<endl;
    cout << "big :"<<setw(space)<<big<<endl;
    cout << "big.print(): "; big.print(); cout << endl;
    cout << n2 << "/"<< n1<< " = "<< n2/n1 <<" rem "<<n2%n1<<endl;
    cout << "fibo("<<fibo<<") = "<<fibo.fibo() << endl;
    cout << "fact("<<fact<<") = "<<fact.fact() << endl;
    cout << "10 + n1 = " << 10 + n1 << endl;
    cout << "n1 + 10 = " << n1 + 10 << endl;
    cout << "(n1 == s1)? --> "<<((n1 == s1)?"true":"false")<<endl;
    cout << "n1++ = ? --> before:"<<n1++<<" after:"<<n1<<endl;
    cout << "++s1 = ? --> before:"<<++s1<<" after:"<<s1<<endl;
    cout << "s2 * big = ? --> "<< s2 * big<<endl;
    cout << "big * s2 = ? --> "<< big * s2<<endl;
}
int main() {
    testUnit();
    return 0;
}

I tried to run the code but I keep getting this error. I attempeted to change the BigInt operator+. I am also unable to change the testUnit function.(https://i.sstatic.net/yrmptM90.jpg) The goal is to overload the different operators and print the results as shown in the testUnit function.