foo.cc: In function 'int rn(int)':
foo.cc:4:21: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
    4 |  if(x%400==0||x%4==0&&x%100!=0) return 1;
      |               ~~~~~~^~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:16:10: error: expected primary-expression before ')' token
   16 |  else if()
      |          ^
foo.cc:16:9: warning: suggest explicit braces to avoid ambiguous 'else' [-Wdangling-else]
   16 |  else if()
      |         ^

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