If as a input parameter we receive a signed int, then there should exist some tests to verify what if we put as input a negative intiger.

Missing "#include " in C++ test cases.

Please, avoid C-Style casting in C++ code

This issue is caused by the test code :)

Please, fix it:

main.cpp:20:21: warning: comparison of integers of different signs: 'int' and 'std::__cxx11::basic_string<char, std::char_traits, std::allocator >::size_type' (aka 'unsigned long') [-Wsign-compare]
for (int i = 0; i < s.size(); i++) setS.insert(s[i]);
~ ^ ~~~~~~~~
1 warning generated.

Please, fix for C++:

main.cpp:26:24: warning: comparison of integers of different signs: 'int' and 'std::__cxx11::basic_string<char, std::char_traits, std::allocator >::size_type' (aka 'unsigned long') [-Wsign-compare]
for(int i = 0; i < y.size(); i++){
~ ^ ~~~~~~~~
1 warning generated.

For C++. I used std::stoi (int) and resolved the kata. After click submit I realized I should return 'long long'. I suggest add some additional test cases for checking proper type :)

Please, fix tests:

main.cpp:75:23: warning: comparison of integers of different signs: 'int' and 'std::array::size_type' (aka 'unsigned long') [-Wsign-compare]
for (int i = 0; i < a.size(); i++) out << a[i] << (i < a.size()-1 ? "," : "");
~ ^ ~~~~~~~~
main.cpp:66:48: note: in instantiation of function template specialization 'operator<<<int, 10>' requested here
cout << start << " - " << end << " : " << expected << endl;
^
main.cpp:75:58: warning: comparison of integers of different signs: 'int' and 'unsigned long' [-Wsign-compare]
for (int i = 0; i < a.size(); i++) out << a[i] << (i < a.size()-1 ? "," : "");
~ ^ ~~~~~~~~~~
2 warnings generated.

Please, fix it:

main.cpp:24:21: warning: comparison of integers of different signs: 'int' and 'std::__cxx11::basic_string<char, std::char_traits, std::allocator >::size_type' (aka 'unsigned long') [-Wsign-compare]
for ( int i=0; i<fight.length(); i++)
~^~~~~~~~~~~~~~~
1 warning generated.

Please, fix it warning for C++:

main.cpp:62:30: warning: comparison of integers of different signs: 'int' and 'unsigned long' [-Wsign-compare]
for(int i = 0; i < numbers.size() - 1; i++)
~ ^ ~~~~~~~~~~~~~~~~~~
1 warning generated.

(warning from test cases, not my code)

Missing "using namespace std;" for C++ Test samples. Imho you shoudln't force devs to use that in them solutions :) - and the "Test samples" should work right away, without any other action.

Please, fix tests for C++:

main.cpp:25:24: warning: comparison of integers of different signs: 'int' and 'std::__cxx11::basic_string<char, std::char_traits, std::allocator >::size_type' (aka 'unsigned long') [-Wsign-compare]
for(int i = 0; i < drone.size(); i++){
~ ^ ~~~~~~~~~~~~
1 warning generated.

Please fix it for C++ (warning from test code, not mine):

main.cpp:53:30: warning: comparison of integers of different signs: 'int' and 'std::__cxx11::basic_string<char, std::char_traits, std::allocator >::size_type' (aka 'unsigned long') [-Wsign-compare]
for(int i = 0; i < str.size(); i++)
~ ^ ~~~~~~~~~~
1 warning generated.

Something is wrong, I had to add "#include " to avoid:

main.cpp:50:5: error: use of undeclared identifier 'strcpy'
strcpy ( ch_digits , conv_num.c_str());
^
1 error generated.