foo.c: In function 'main':
foo.c:8:9: warning: 'days' is used uninitialized [-Wuninitialized]
    8 |         printf("该年该月的天数为：%d\n",days);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.c:4:24: note: 'days' was declared here
    4 |         int year,month,days;
      |                        ^~~~

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