I'd like to give your some tips. First, change your code a bit, iostream.h library was deprecated for several years. Use "using namespace std" instead. Here is an example of the above code:
using namespace std;
int main (void)
cin >> someInput;
cout << someInput;
I'm assuming that you've saved this file as input.cc. Compile it with g++, like this:
g++ -o program input.cc
That would create an executable file called "program". Execute it with "./program". That should work.