How to write a matrix into csv C++

Question

I'm a new learner of C++. I want to get a CSV file like this:

   |  S0001    |   S0002   | S0003  | S0004  |  ...
0  | 10.289461 | 17.012874 |        |
1  | 11.491483 | 13.053712 |        |
2  | 10.404887 | 12.190057 |        | 
3  | 10.502540 | 16.363996 | ...    |  ...
4  | 11.102104 | 12.795502 |        | 
5  | 13.205706 | 13.707030 |        |
6  | 10.544555 | 12.173467 |        | 
7  | 10.380928 | 12.578932 |        | 
8  | 10.962240 | 12.615608 |        | 
9  | 10.690547 | 17.678212 |        | 
10 | 12.416197 | 13.769609 |        |
...    ...         ...         ...     ...  

The first column is a series of integers. The cell values are generated from a log-normal distribution.

Here is my code:

#include <iostream>
#include <vector>
#include <random> 
#include <fstream>
#include <stream>

//get first row: S0001, S0002, S0003, etc
std::string GetNextNumber(int lastNum)
{
    std::stringstream ss;
    ss << "S";
    ss << std::setfill('0') << std::setw(4) << lastNum;
    return ss.str();
}
int main()
{
    std::string ukey;
    int ticktime;
    double bid;
    double len = 1000;
    
    std::default_random_engine generator;
    std::lognormal_distribution<double> distribution(0.0,1.0);
    
    std::ofstream outFile;
    outFile.open("Data_bid.csv");
    
    for(int j=0; j<50; ++j){ 
        ukey = GetNextNumber(j+1);
        outFile<<","<<ukey;
    }
    outFile<<std::endl;
    for(int i=0; i<len; ++i){       
        ticktime = i;
        bid = distribution(generator)+10;
        outFile<<ticktime<<","<<bid<<std::endl;
    }   
    outFile.close();

    return 0;
} 

Right now, the code can only give me a result like this:

I don't know how to append values for the rest of the columns. Can you help me out or provide some other methods to write the csv?

Answer 1

Thank you for @paddy 's hint and here is my own solution:

for(int i=0; i<len; ++i){       
    ticktime = i;
    outFile<<ticktime;
    for(int j=0; j<50; ++j){ 
        bid = distribution(generator)+10;
        outFile<<","<<bid;
    }
    outFile<<std::endl;
}