Decompression (w/o sstream) C++

#include <iostream>
#include <string>

int main()
{
    using namespace std;

    string szInput;
    getline(cin, szInput);

    for (int i = 0; i < szInput.length(); i++)
    {
        char ch = szInput[i];
        int nCurNum = 0;
        while (ch >= '0' && ch <= '9')
        {
            if (!nCurNum)
                nCurNum = ch - '0';
            else
                nCurNum = 10 * nCurNum + ch - '0';
            ch = szInput[++i];
        }

        if (!nCurNum)
            nCurNum = 1;

        cout << string(nCurNum, ch);
    }

    cout << endl;

    return 0;
}