String Fibonacci Algorithm

//This Programme returns the Nth fibonacci as a string.
//The method used is manual addition with carry and placing it in a string which is called string addition
//This makes it have no bounds or limits

#include <iostream>
#include <string>

using namespace std;

string add(string a, string b)
{
    string temp = "";

    // carry flag
    int carry = 0;

    // fills up with zeros
    while ((int)a.length() < (int)b.length())
    {
        a = "0" + a;
    }

    // fills up with zeros
    while ((int)b.length() < (int)a.length())
    {
        b = "0" + b;
    }

    // adds the numbers a and b
    for (int i = a.length() - 1; i >= 0; i--)
    {
        char val = (char)(((a[i] - 48) + (b[i] - 48)) + 48 + carry);
        if (val > 57)
        {
            carry = 1;
            val -= 10;
        }
        else
        {
            carry = 0;
        }
        temp = val + temp;
    }

    // processes the carry flag
    if (carry == 1)
    {
        temp = "1" + temp;
    }

    // removes leading zeros.
    while (temp[0] == '0' && temp.length() > 1)
    {
        temp = temp.substr(1);
    }

    return temp;
}

void fib_Accurate(long long n)
{
    string tmp = "";
    string fibMinus1 = "1";
    string fibMinus2 = "0";
    for (long long i = 0; i < n; i++)
    {
        tmp = add(fibMinus1, fibMinus2);
        fibMinus2 = fibMinus1;
        fibMinus1 = tmp;
    }
    cout << fibMinus2;
}

int main()
{
    int n;
    cout << "Enter whatever number N you want to find the fibonacci of\n";
    cin >> n;
    cout << n << " th Fibonacci is \n";
    fib_Accurate(n);

    return 0;
}