foo.c: In function 'main':
foo.c:7:5: warning: unused variable 'yearday' [-Wunused-variable]
 int yearday,year,month=0,day=0;
     ^~~~~~~
foo.c:10:1: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
 scanf("%d%d%d",&cu_year,&cu_month,&cu_day);
 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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