foo.cc: In function ‘bool a(int)’:
foo.cc:6:22: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
    6 |         return y%4==0&&y%100!=0||y%400==0;
      |                ~~~~~~^~~~~~~~~~
foo.cc: In function ‘int add(int, int)’:
foo.cc:29:26: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
   29 |                 if(i%4==0&&i%100!=0||i%400==0)
      |                    ~~~~~~^~~~~~~~~~