can anyone tell me why this outputs backwards

This is a discussion on can anyone tell me why this outputs backwards within the C++ Programming forums, part of the General Programming Boards category; Code: #include <iostream> #include <vector> #include <string> using namespace std; vector<string> store_all_substrings(string s) { if(s.length() <= 1) { vector<string> single_letter; ...

  1. #1
    Registered User
    Join Date
    May 2010
    Posts
    4

    can anyone tell me why this outputs backwards

    Code:
    #include <iostream>
    #include <vector>
    #include <string>
    
    using namespace std;
    
    
    vector<string> store_all_substrings(string s)
    {
       
       if(s.length() <= 1)
       {
         vector<string> single_letter;
          single_letter.push_back(s);
          return single_letter;
       }
        vector<string> all_substrings = store_all_substrings(s.substr(1)); 
       for (int i = 1; i <= s.length(); i++)
        all_substrings.push_back(s.substr(0, i));
         
       return all_substrings;
    }
    
    int main()
    {
    
      vector<string> all_substrings = store_all_substrings("cat");
      for(int i = 0; i < all_substrings.size(); i++)
         cout << all_substrings[i] << "\n";
       
       return 0;
    }

  2. #2
    and the Hat of Guessing tabstop's Avatar
    Join Date
    Nov 2007
    Posts
    14,185
    It prints out in the order you build the vector. If that's not the order you want to print them, then either (a) build the vector in the opposite order (b) use reverse to reverse the vector (c) pick a container that supports push_front instead.

  3. #3
    Registered User
    Join Date
    Oct 2008
    Posts
    1,262
    I think his problem is that the strings generated in:
    Code:
    store_all_substrings(s.substr(1));
    Are stored before the substrings of the current string.

    Honestly, I'd make the prototype:
    Code:
    void store_all_substrings(vector<string> &result, const string &s)
    To make it faster and easier to read, as you don't have to copy as much from vector to vector; all you have to do is push_back.

    But the actual problem is that you "store all substrings" of s.substr(1) before you generate the substrings of "s". If you wanted it reversed, first do the substrings of s and then the other thing.

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