Tìm chỗ sai hộ em với mn !!!

#include<stdio.h>
const int minyear=1900, maxyear=10000;
int kiemtranamnhuan(int year)
{
int kq;
if(year < minyear || year > maxyear)
kq= -1;
else if(year%4!=0) kq=0;
else if(year%100!=0) kq=1;
else if(year%400==0) kq=1;
else kq=0;
return kq;
}
int xuatnam(int year)
{
int kq;
if(kq==1) printf("nam nhuan\n");
if(kq==0) printf("nam k nhuan\n");
else if(kq==-1) printf("nhap lai nam\n");
}
int songaytrongthag(int thang)
{
int songay,year;
switch(thang)
{
case 1:songay=31; break;
case 3:songay=31; break;
case 5: songay=31; break;
case 7:songay=31; break;
case 8: songay=31; break;
case 10: songay=31; break;
case 12: songay=31; break;
case 4: songay=30; break;
case 6:songay=30; break;
case 9:songay=30; break;
case 11: songay=30; break;
case 2:
{
if(kiemtranamnhuan(year)==1) songay=29;
else
if(kiemtranamnhuan(year)==0) songay=28;
}
default:
if (thang<1||thang>12) break;
}
return songay;
}
int main()
{
int year,songay,thang;
printf("nhap vao nam:");
scanf("%d",&year);
printf("nhap vao thang:");
scanf("%d",&thang);
kiemtranamnhuan(year);
xuatnam(year);
songaytrongthag(thang);
printf("%d\n",songay);
}