Программы разветленной структуры: определить день недели с датой D и M

#include<iostream.h>
int d;
int main()
{ cout<<"Day";cin>>d;
switch(d)
{
 case 1:cout<<"Понедельник";break;
 case 2:cout<<"Вторник";break;
 case 3:cout<<"Среда";break;
 case 4:cout<<"Четверг";break;
 case 5:cout<<"Пятница";break;
 case 6:cout<<"Суббота";break;
 case 7:cout<<"Воскресенье";break;
 default: cout<<"Не день";
}

unsigned month_length(unsigned m) {
    unsigned len;
    switch (--m) {
    case 1: case 2: case 3: case  4: case  5: case  6:
    case 7: case 8: case 9: case 10: case 11: case 12:
    {
        unsigned l[] = { 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
        len = l[m] + month_length(m);
    }
    break;
    default:
        len = 0;
        break;
    }
    return len;
};
 
unsigned day_of_week(unsigned d, unsigned m, unsigned w) {
    unsigned dofy = w + d - 1;
    dofy += month_length(m);
    dofy %= 7;
    if (dofy > 0)
        return dofy;
    return 7;
}
 
#include <cstdio>
 
int main() {
    printf("%u", day_of_week(21, 12, 3));
    return 0;
}

int days[12]={31,28,31,30,31,30,31,31,30,31,30,31};
int D=10;
int M=7;
int W=3;
int TotalDays=D+W;
for(int i=0;i<M-1;i++)
   TotalDays+=days[i];
cout<<TotalDays%7;