C++ Reduce Fractions

#include <iostream>
#include <string>
#include <sstream>

using namespace std;

long gcd(long, long);
string doFrac(double, double);
int countDigits(double);

int main(){
  cout << doFrac(66,20);
}

long gcd(long a, long b){
    if (a == 0)
        return b;
    else if (b == 0)
        return a;

    if (a < b)
        return gcd(a, b % a);
    else
        return gcd(b, a % b);
}

string doFrac(double num, double denom){
    ostringstream s;
    string re;
    double dec;
    long gcd_;

    dec = num / denom;

    if(countDigits(dec) < 7){
        dec *= 100;
        gcd_ = gcd(dec, 100);

        dec /= gcd_;
        int dec2 = dec;
        double temp = 100 / gcd_;
        s << dec2; s << "/"; s << temp;
        re = s.str();
        return re;
    } else {
        int nDec = 0;
        int nine = 0;
        if(gcd(num, denom) == 1){
            s << num; s << "/"; s << denom;
            re = s.str();
            return re;
        } else {
            dec *= 10;
            nDec = dec;
            nine = 9 /gcd(nDec, 9);
            nDec /= gcd(nDec, 9);
            s << nDec; s << "/"; s << nine;
            re = s.str();
            return re;
        }
    }
}

int countDigits(double d){
    ostringstream s1;
    string s2;
    s1 << d;
    s2 = s1.str();
    int num;
    for(int i = 0; i < s2.size(); i++){
        num++;
    }
    return abs(num);
}
int countDigits(int d){
    ostringstream s1;
    string s2;
    s1 << d;
    s2 = s1.str();
    int num;
    for(int i = 0; i < s2.size(); i++){
        num++;
    }
    return num;
}