c语言 已知1900.1.1是周一 输入年月日判断是星期几

#include
main()
{
    int n,y,r,k=0,a,b,h=0;
    scanf("%d%d%d",&n,&y,&r);
    if(n%100!=0&&n%4==0||n%400==0)
    {
        switch(y)
        {
            case 12:k=k+30;
            case 11:k=k+31;
            case 10:k=k+30;
            case 9:k=k+31;
            case 8:k=k+31;
            case 7:k=k+30;
            case 6:k=k+31;
            case 5:k=k+30;
            case 4:k=k+31;
            case 3:k=k+29;
            case 2:k=k+31;
        }
    }
    else
    {
        switch(y)
        {
            case 12:k=k+30;
            case 11:k=k+31;
            case 10:k=k+30;
            case 9:k=k+31;
            case 8:k=k+31;
            case 7:k=k+30;
            case 6:k=k+31;
            case 5:k=k+30;
            case 4:k=k+31;
            case 3:k=k+29;
            case 2:k=k+31;
        }
    }
    a=k+r;
    for(b=1900;b    {
        if(b%100!=0&&b%4==0||b%400==0)
            h=h+366;
        else
            h=h+365;
    }
    if((a+h-1)%7==0)
        printf("0");
    else
        printf("%d",(a+h-1)%7);
}