/in/foo.cc:2:5: error: cannot declare '::main' to be a global variable
 int main{
     ^~~~
/in/foo.cc:3:2: error: expected primary-expression before 'int'
  int a,b;
  ^~~
/in/foo.cc:3:2: error: expected '}' before 'int'
/in/foo.cc:4:7: error: expected constructor, destructor, or type conversion before '(' token
  scanf("%d %d",&a,&b);
       ^
/in/foo.cc:5:8: error: expected constructor, destructor, or type conversion before '(' token
  printf("%d\n",a+b);
        ^
/in/foo.cc:6:2: error: expected unqualified-id before 'return'
  return 0;
  ^~~~~~
/in/foo.cc:7:1: error: expected declaration before '}' token
 }
 ^