"Pop quiz! What will the following program return? int main() { printf("Hello World!\n"); } In C99 or later, it produces a mandatory d

"Pop quiz! What will the following program return? int main() { printf("Hello World!\n"); } In C99 or later, it produces a mandatory diagnostic because `printf` is not declared. In C90, it has undefined behavior because a variadic function is called with no visible prototype.