foo.cc: In function 'int main()':
foo.cc:9:27: error: 'o' was not declared in this scope
  if(year%400==0||(year%4==o&&year%100!=0))
                           ^
foo.cc:18:1: error: 'else' without a previous 'if'
 else if(month==1||month==3||month==4||month==5||month==7||month==8||month==10||month==12)
 ^~~~
foo.cc:23:1: error: expected ';' before 'return'
 return 0;
 ^~~~~~

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