$ cat k.cpp
template<typename T, typename... Args>
T sum(T x, Args... args) {
    return x + sum(args...);

}

template<typename T>
T sum(T x) {
    return x;
}

int main() {
    sum(1, 2, 3, 4, 5);

}

20:24:03 - 0
[- desktop@/tmp -]
$ g++ k.c
k.c:2:1: warning: ISO C++ forbids declaration of ‘main’ with no type [-Wreturn-type]
    2 | main ()
      | ^~~~
k.c: In function ‘int main()’:
k.c:4:17: error: initializer-string for ‘char [6]’ is too long [-fpermissive]
    4 |     char x[6] = "12345\0";
      |                 ^~~~~~~~~
k.c:5:17: error: initializer-string for ‘char [6]’ is too long [-fpermissive]
    5 |     char y[6] = "67890\0";
      |                 ^~~~~~~~~