foo.cc: In function ‘int main()’:
foo.cc:8:14: error: lvalue required as left operand of assignment
    8 |         if((a%4=0&&a%100!=0)||a%400=0)
      |             ~^~
foo.cc:9:49: error: lvalue required as left operand of assignment
    9 |                 if(b=1||b=3||b=5||b=7||b=8||b=10||b=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:16:49: error: lvalue required as left operand of assignment
   16 |                 if(b=1||b=3||b=5||b=7||b=8||b=10||b=12)
      |                                               ~~^~~
foo.cc:18:26: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
   18 |                 else if(b=4||6||9||11)
      |                         ~^~~~~~~~~~~~