Summing Fractions

[SamEvans3]

Hi there, there is a small bug in my code that I cannot quite figure out.
- The input starts with the number of fractions you want to add (eg. 3)
- You can then input fractions in the form of
1) A while number (eg. 2)
2) A fraction (eg. 1/2)
3) A mixed number (e.g. 3,4/5)
- The program keeps a running numerator and denominator
- Then at the end it will say in the lowest form the added fraction
It appears to work but for some test cases it proves false and I do not know which ones.
Does anything appear wrong?
Thankyou

using namespace std;

int GCD(int a, int b)
{
    int r = a%b;
    if (r!=0)
    {
        return GCD(b, r);
    }
    return b;
}


int main()
{
    for (int b = 0; 1; b++)
    {
        int numbers;
        cin >> numbers;
        cin.ignore();
        if (numbers<1)
        {
            break;
        }
        int top = 0;
        int bottom = 1;
        for (int a = 0; a<numbers; a++)
        {
            int tmpTop;
            int tmpBottom;
            string line;
            getline(cin, line);
            stringstream is;
            if (count(line.begin(), line.end(), ',')==1)
            {
                // Is a mixed fraction
                replace(line.begin(), line.end(), ',', ' ');
                replace(line.begin(), line.end(), '/', ' ');
                is << line;
                int tmp;
                is >> tmp;
                is >> tmpTop;
                is >> tmpBottom;
                tmpTop = tmpTop + (tmp*tmpBottom);
                if (a==0)
                {
                    top = tmpTop;
                    bottom = tmpBottom;
                }
                else
                {
                    top = (top*tmpBottom)+(tmpTop*bottom);
                    bottom = (bottom*tmpBottom);
                }
            }
            else
            {
                if (count(line.begin(), line.end(), '/')==1)
                {
                    // Is a fraction
                    replace(line.begin(), line.end(), '/', ' ');
                    is << line;
                    is >> tmpTop;
                    is >> tmpBottom;
                    if (a==0)
                    {
                        top = tmpTop;
                        bottom = tmpBottom;
                    }
                    else
                    {
                        top = (top*tmpBottom)+(tmpTop*bottom);
                        bottom = (bottom*tmpBottom);
                    }
                }
                else
                {
                    // Is a whole number
                    is << line;
                    is >> tmpTop;
                    tmpBottom = 1;
                    if (a==0)
                    {
                        top = tmpTop;
                        bottom = tmpBottom;
                    }
                    else
                    {
                        top = (top*tmpBottom)+(tmpTop*bottom);
                        bottom = (bottom*tmpBottom);
                    }
                }
            }
        }
        cout << "Case " << b+1 << ": " << top << "/" << bottom << endl;
        if (top==0)
        {
            // It's one
            cout << "Test " << b+1 << ": 0" << endl;
        }
        else
        {
            if (top==bottom)
            {
                // It's zero
                cout << "Test " << b+1 << ": 1" << endl;
            }
            else
            {
                if (top>bottom)
                {
                    int tmp = top/bottom;
                    top = top - (bottom*tmp);
                    int common = GCD(top, bottom);
                    top = top/common;
                    bottom = bottom/common;
                    if (top==0)
                    {
                        cout << "Test " << b+1 << ": " << tmp << endl;
                    }
                    else
                    {
                        cout << "Test " << b+1 << ": " << tmp << "," << top << "/" << bottom << endl;
                    }
                }
                else
                {
                    int common = GCD(top, bottom);
                    top = top/common;
                    bottom = bottom/common;
                    cout << "Test " << b+1 << ": " << top << "/" << bottom << endl;
                }
            }
        }
    }
    return 0;
}