foo.cc: In function ‘int main()’:
foo.cc:8:19: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
    8 |     if(n % 4 == 0 && n % 100 != 0 || n % 400 == 0)
      |        ~~~~~~~~~~~^~~~~~~~~~~~~~~
foo.cc:6:13: warning: unused variable ‘r’ [-Wunused-variable]
    6 |     int n,y,r;
      |             ^