c++ - Xcode 6 Beta 3 Unusable Variable Issue -

so novice c++ programmer, , have never coded on macos. using xcode 6 beta 3 , getting unusable variable error whenever want name variable integer.

my setup looks this

#include <iostream> using namespace std; int main () {     int a;     cout << "hello world!" << endl;     return 0; } 

i getting warning sign beside int a; saying unusable variable. why that?

also because such novice question perhaps direct me solid xcode 6 tutorials teach me how code in command line.