How to manage and write code to : call and or open and or execute something?

Question

It seems a very simple and basic question but i have problems with compiler while doing this!

I use nearly latest version of g++ but ... :
1- whenever i try to use another program to enter ..
compiler gives error message about lack of declaration or definition of that program-name ..
Unfortunately those program-names mostly are compiled previously by the same compiler! .. and i think compiler should have enough knowledge about them ..
Also compiler has no knowledge about itself!
also about c++
Finall

Answer 1

... original question is continued here!!
...
Finally when i declare that .. usually errors about unqualified id is the result
2- when i write a file-name to be openned .. sometimes that file is not found due to being hidden then i have to write the URL .. in such cases compiler outputs aother error messages about stray in program .. then how do i write an address or URL while coding?!

Answer 2

Пробелы в названиях есть? У меня Lubuntu 16.10 и последняя версия g++. Всё работает. Проверь названия файлов.

Answer 3

For a long time i have been using Mandriva2012 and due to some reasons i can not change OS!