Inputting into files and outputting to another file and passing ofstream files to functions

Question

Pretext: I am new to c++ coding and know arrays and strings. This professor showed how to input and output into files and gave us the following assignment.

Assignment question: Input a number in a file. Now imagine there is a staircase with the inputted number of steps. You can either step up one step and denote this by 'u' or you can take two steps up and denote this by 'd'. Find all possible combinations of this type and write them in a file.

Example: For n=1 the output should be 'u'; For n=2 the output should be 'uu d'; For n=3 the output should be 'uuu ud du' and so on.

My thought process: So this is basically a Fibonacci series. So just like fibonacci series i thought of a recursive algorithm. Here is what I came up with...

Code

#include<iostream>
#include<fstream>
using namespace std;
void staircase(int num, int count, char* c, int index, ofstream &file)
{
    char c1[num], c2[num];    
    for (int i = 0;i < num;i++) {
        c1[i] = c[i];
        c2[i] = c[i];
    }
    if (num - count == 2) {
        c1[index] = 'd';
        c2[index] = 'u';
        c2[index + 1] = 'u';
        file.open("output.txt", ios::app);
        file << c1 <<"  ";
        file << c2 <<"  ";
        file.close();
        return;


    }
    if (num - count == 1) {
        c2[index] = 'u';
        file.open("output.txt", ios::app);
        file << c2 <<"  ";
        file.close();
        return;

    }
    if (num - count > 2) {
        c1[index] = 'd';
        c2[index] = 'u';
        staircase(num, count + 2, c1, index+1,file);
        staircase(num, count + 1, c2, index+1,file);
    }
}
int main(){
    int num;
    cout<<"Input total number of stairs: ";
    cin>>num;
    fstream myfile;
    myfile.open("input.txt");
    myfile<<num;
    myfile.close();
    cout<<"Input is saved in file Directory   ";
    char c[num];
    ofstream file;
    file.open("output.txt");
    staircase(num, 0, c, 0, file);
}

Problem: When I wrote it without the file code and all it did fine and command prompt showed all the possible outputs. I also noticed for n=1 and n=2 it doesn't even print anything on the file. I feel like I'm missing somethings with fstream and cannot point it down. I tried to search google and stackoverflow. Thanks for helping me. Also following is the version without any files in it.

#include<iostream>
#include<fstream>
using namespace std;
void staircase(int num, int count, char* c, int index)
{
    char c1[num], c2[num];    
    for (int i = 0;i < num;i++) {
        c1[i] = c[i];
        c2[i] = c[i];
    }
    if (num - count == 2) {
        c1[index] = 'd';
        c2[index] = 'u';
        c2[index + 1] = 'u';
        for(int i=0;i<=index;i++)
        cout<<c1[i];
        cout<<" ";
        for(int i=0;i<=index+1;i++)
        cout<<c2[i];
        cout<<" ";
        return;


    }
    if (num - count == 1) {
        c2[index] = 'u';
        for(int i=0;i<index+1;i++)
        cout<<c2[i];
        cout<<" ";
        return;

    }
    if (num - count > 2) {
        c1[index] = 'd';
        c2[index] = 'u';
        staircase(num, count + 2, c1, index+1);
        staircase(num, count + 1, c2, index+1);

    }
}
int main(){
    int num;
    cout<<"Input total number of stairs: ";
    cin>>num;
    cout<<"Input is saved in file Directory   ";
    char c[num];
    staircase(num, 0, c, 0);
}

Answer 1

In your description of the problem it sounds like the version streaming to std::cout does the job correctly. In that case, just add a parameter to staircase taking a std::ostream& and replace cout everywhere in the function with the ostream parameter. That way you can stream both to std::cout and opened std::ofstreams.

If you want to stay with standard C++, don't use VLA:s - use a std::vector<> instead. It has a lot of nice features, such as a member function called size() that you can use instead of having to pass num as a separate parameter together with your VLA.

Example:

#include <cstddef>
#include <fstream>
#include <iostream>
#include <vector>

// When using a vector, you don't need to pass in "num". The vector
// has a size() function that returns how many enements it contains.
// Also note the added std::ostream parameter for streaming to any ostream.
void staircase(size_t count, const std::vector<char>& c, size_t index, std::ostream& os)
{
    std::vector<char> c1 = c; // create a copy of c instead of manual looping
    std::vector<char> c2 = c; // create a copy of c instead of manual looping

    if(c.size() - count == 2) {
        c1[index] = 'd';
        c2[index] = 'u';
        c2[index + 1] = 'u';
        for(size_t i = 0; i <= index; ++i) os << c1[i];
        os << ' ';
        for(size_t i = 0; i <= index + 1; ++i) os << c2[i];
        os << ' ';
        return;
    }
    if(c.size() - count == 1) {
        c2[index] = 'u';
        for(size_t i = 0; i < index + 1; ++i) os << c2[i];
        os << ' ';
        return;
    }
    if(c.size() - count > 2) {
        c1[index] = 'd';
        c2[index] = 'u';
        staircase(count + 2, c1, index + 1, os);
        staircase(count + 1, c2, index + 1, os);
    }
}

int main() {
    size_t num;
    std::cout << "Input total number of stairs: ";
    std::cin >> num;

    // use a vector instead of a VLA:
    std::vector<char> c(num, 0);

    // Just call staircase with an open file instead of std::cout
    // if you want the output to a file.
    staircase(0, c, 0, std::cout);

    std::cout << '\n';
}