foo.c: In function 'main':
foo.c:20:37: error: 'o' undeclared (first use in this function)
   20 |             if(year%400==0||year%4==o&&year%100!=0)
      |                                     ^
foo.c:20:37: note: each undeclared identifier is reported only once for each function it appears in
foo.c:22:10: warning: this 'else' clause does not guard... [-Wmisleading-indentation]
   22 |          else
      |          ^~~~
foo.c:23:25: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'else'
   23 |                  day=28;break;
      |                         ^~~~~
foo.c:26:9: warning: implicit declaration of function 'print'; did you mean 'printf'? [-Wimplicit-function-declaration]
   26 |         print("%d",day);
      |         ^~~~~
      |         printf

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