DecodeNumToString

/*
http://www.careercup.com/question?id=19300678
If a=1, b=2, c=3,....z=26. Given a string, find all possible codes that string can generate. Give a count as well as print the strings. 
 
For example: 
Input: "1123". You need to general all valid alphabet codes from this string. 
 
Output List 
aabc //a = 1, a = 1, b = 2, c = 3 
kbc // since k is 11, b = 2, c= 3 
alc // a = 1, l = 12, c = 3 
aaw // a= 1, a =1, w= 23 
kw // k = 11, w = 23
*/
#include <vector>
#include <iostream>
#include <string>
using namespace std;
 
void helper(const string &num, int idx, string &tmp, int &count)
{
    if (idx == num.length())
    {
        count++;
        cout << tmp << endl;
    }
    else
    {
        if ((num[idx] == '1' && (idx + 1) != num.length())
            || (num[idx] == '2' && (idx + 1) != num.length() && num[idx + 1] <= '6'))
        {
            char c = (char)((num[idx] - '0') * 10 + num[idx + 1] - '0' + 'a' - 1);
            string tmp1 = tmp + c;
            helper(num, idx + 2, tmp1, count);
        }
        char c = (char)(num[idx] - '0' + 'a' - 1);
        string tmp2 = tmp + c;
        helper(num, idx + 1, tmp2, count);
    }
} 
 
// return the count
int convertAndCount(const string &num)
{
    string result;
    int count = 0;
    helper(num, 0, result, count);
    return count;
}
 
int main()
{
    int count = convertAndCount("1123");
    cout << count << en);
    return 0;
}

use decode() instead of convert()