为什么这个会生成两个days

#include <stdio.h>

int monthDays(int year, int month) ;

int main() {
    int year,month;
    scanf("%d %d", &year,&month);
    printf("days = %d\n", monthDays(year,month));
}

/* 请在这里填写答案 */
int monthDays(int year, int month){
	int days=0;
	switch(month){
	case 1:
	case 3:
	case 5:
	case 7:
	case 8:
	case 10:
	case 12:days=31; break;
	case 11:
	case 4:
	case 6:
	case 9: days=30;break;
	case 2:
	if((year%4==0&&year%100!=0)||year%400==0) days=29;
	else days=28;
	
	printf("days=%d",days);
}
}