How is this line returning the length of the array in recursion?

Question

I am trying to understand this recursion using the debugger and trying to understand it step by step the main.The debugger shows the smallAns returns the size of the array I can't understand how this smallAns is returning the size of the array input[].can anyone explain this

 #include<iostream>
    using namespace std;
    int subsequences(char input[], int startIndex,char output[][50]){
          if(input[startIndex] == '\0'){
            output[0][0] = '\0';
            return 1;
          }
          int smallAns = subsequences(input, startIndex+1, output);
          for(int i = smallAns; i < 2*smallAns; i++){
            int row = i - smallAns;
            output[i][0] = input[startIndex];
            int j = 0;
            for(; output[row][j] != '\0'; j++){
                output[i][j + 1] = output[row][j];
            }
            output[i][j + 1] = '\0';
          }
          return 2*smallAns;
        }
        int main(){

      char input[] = "abc";
      char output[100][50];
      int ans = subsequences(input, 0, output);
      for(int i = 0; i < ans; i++){
        for(int j = 0; output[i][j] != '\0'; j++){
          cout << output[i][j];
        }
        cout << endl;
      }
    }

Answer 1

Here's what the algorithm is doing:

Start at the end, with the empty subsequence (or "\0"). You have 1 subsequence.

Look at the last character not yet considered. For all the subsequences you have found, you can either add this last character, or don't. Therefore you have doubled the number of subsequences.

Repeat.

Therefore, 2 * smallAns means "Take the number of subsequences found in the lower recursive call, and double it." And this makes sense after you know how it was implemented. Thus the importance of comments and documentation in code. :)