foo.c: In function ‘main’:
foo.c:21:21: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
   21 |         if(year%4==0&&year%100!=0||year%400==0)
      |            ~~~~~~~~~^~~~~~~~~~~~~
foo.c:25:12: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
   25 |         if(year=1&&month>2)
      |            ^~~~
foo.c:4:32: warning: variable ‘leap’ set but not used [-Wunused-but-set-variable]
    4 |         int year,month,day,sum,leap;
      |                                ^~~~
foo.c:27:20: warning: ‘sum’ may be used uninitialized [-Wmaybe-uninitialized]
   27 |                 sum++;
      |                 ~~~^~
foo.c:4:28: note: ‘sum’ was declared here
    4 |         int year,month,day,sum,leap;
      |                            ^~~