Symbol std could not be resovled Eclipse Mars C/C++

Question

I installed Eclipse Mars on Ubuntu 14.04. When I try create an empty project and simple program I get the error "Symbol std could not be resovled" , and the same forcout. But when I run the Hello world project included in Eclipse, everything works fine. What might be the problem?

Current toolchain : Linux GCC
Current builder : GNU make builder
GCC Archiver
GCC C++ Compiler
GCC C Compiler
GCC C Linker
GCC C++ Linker
GCC Assembler

Example code:

#include <iostream> 
using namespace std; 
int main() 
{ 
    cout << "Hello"; 
    return 0; 
}