数学编写程序问题

编写程序，将用户输入的正整数转换成相应的星期值输出.如用户输入3，则输出Wednesday；用户输入0，则输出Sunday，如果用户输入的数大于6，则用这个数除以7所得的余数进行上述操作。

#include <iostream>
using namespace std;

void main() {
int n;
cout << "enter your number:\n"
cin >> n;
if(n<0) { cerr << "bad input.\n"; return; }
switch(n%7) {
case 0: cout << "Sunday\n"; break;
case 1: cout << "Monday\n"; break;
case 2: cout << "Tuesday\n"; break;
case 3: cout << "Wednesday\n"; break;
case 4: cout << "Thirsday\n"; break;
case 5: cout << "Friday\n"; break;
case 6: cout << "Saturday\n"; break;
default: cout << "whoops...\n";
}
}

C++直接写的，没经过测试。

main(){
int day,num;
scanf("%d",&num);
day = num%7;
switch (day)
{
case 0 : printf("Sunday\n");
break;