foo.cc: In function ‘int main()’:
foo.cc:8:17: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
    8 |         if(a%4=0&&a%100!=0||a%400=0)
      |                ~^~~~~~~~~~
foo.cc:8:27: error: lvalue required as left operand of assignment
    8 |         if(a%4=0&&a%100!=0||a%400=0)
      |                ~~~~~~~~~~~^~~~~~~
foo.cc:9:21: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
    9 |                 if(b=1||3||5||7||8||10||12)
      |                    ~^~~~~~~~~~~~~~~~~~~~~~
foo.cc:11:26: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
   11 |                 else if(b=4||6||9||11)
      |                         ~^~~~~~~~~~~~
foo.cc:16:21: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
   16 |                 if(b=1||3||5||7||8||10||12)
      |                    ~^~~~~~~~~~~~~~~~~~~~~~
foo.cc:18:26: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
   18 |                 else if(b=4||6||9||11)
      |                         ~^~~~~~~~~~~~