$ cat sleepwarn.cpp && g++ -Wall -Wextra sleepwarn.cpp 
#include <iostream>
int main() {
  int i = 0;
  while (i++ < 10); {
    std::cout << i;
  }
}
sleepwarn.cpp: In function ‘int main()’:
sleepwarn.cpp:4: warning: suggest a space before ‘;’ or explicit braces around empty body in ‘while’ statement