Test filename generator

#include <iostream>
#include <cstring>
#include <vector>
#include <algorithm>
using namespace std;


char *filename(int len1, int len2) //returns name for the output file: res_<first sequence length>_<second sequence length>.csv
{
    char *ans = new char[16];
    strcpy(ans, "res_");
    vector<int> num;
    while (len1 > 0)
    {
        num.push_back(len1%10);
        len1 /= 10;
    }
    reverse(num.begin(), num.end());
    for (int x: num)
    {
        char *s3 = new char;
        *s3 = (char) ((int) '0' + x);
        strcat(ans, s3);
    }
    strcat(ans, "_");
    num.clear();
    while (len2 > 0)
    {
        num.push_back(len2%10);
        len2 /= 10;
    }
    reverse(num.begin(), num.end());
    for (int x: num)
    {
        char *s3 = new char;
        *s3 = (char) ((int) '0' + x);
        strcat(ans, s3);
    }
    strcat(ans, ".csv");
    return ans;
}

int main()
{
    for (int i = 1; i < 5; i++)
        for (int j = 1; j < 7; j++)
            cout << filename(i, j) << "\n";
    return 0;
}