Defensive Programming Squad

In this thread we pick up innocent programs and tank the shit out of them.

#include <stdio.h>
int main () {
  int n1, n2;
  printf("First integer:");
  scanf("%d", &n1);
  printf("Second integer:");
  scanf("%d", &n2);
  printf("Sum = %d\n", n1+n2);
  return 0;
}

>>9 The main declaration is invalid C99 code.

It's not invalid if gcc doesn't produce a warning:
~ $ echo "int main() {}" | gcc -c -std=c99 -Wall -Wextra -pedantic -xc -o main.o -
~ $