foo.c:2:1: warning: return type defaults to 'int' [-Wimplicit-int]
 main()
 ^~~~
foo.c: In function 'main':
foo.c:5:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d,%d,%d", &year,&month,&day);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.c:26:25: warning: 'r' may be used uninitialized in this function [-Wmaybe-uninitialized]
  sum=(2021-year-r)*365+r*366+month+day;
                        ~^~~~

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