/in/foo.cc: In function 'int calculateGCD(int*)':
/in/foo.cc:10:22: error: 'gcd' was not declared in this scope
         r=gcd(r, a[i]);
                      ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:18:5: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
     if (n <= 0) 
     ^~
/in/foo.cc:20:2: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'if'
  int numbers[n];
  ^~~