如何解决输出值后面多出一个O

#include <bits/stdc++.h>
using namespace std;
int main()
{
int i,j,n;
int m;
cin>>m;
while(m--)
{

scanf("%d %d",&i,&j);

switch(j)
{
    case 1: n=31;
        break;
    case 2:
    {
        if(i%4==0){ n=29;}
        else {n=28;}
    }
        break;
    case 3: n=31;
        break;
    case 4: n=30;
        break;
    case 5: n=31;
        break;
    case 6: n=30;
        break;
    case 7: n=31;
        break;
    case 8: n=31;
        break;
    case 9: n=30;
        break;
    case 10: n=31;
        break;
    case 11: n=30;
        break;
    case 12: n=31;
        break;

default:printf("ERROR\n");
}
printf("%d\n",n); }
return 0;
}

本应该输出的是ERROR但是后面会多出来一个O，这是怎么回事呀,这是一个求某年某个月的天数的代码

几处修改见注释，供参考：

#include <iostream>
//#include <bits/stdc++.h>
using namespace std;
int main()
{
    int i, j, n;
    int m;
    cin >> m;
    while (m--)
    {

        scanf("%d %d", &i, &j);

        switch (j)
        {
        case 1: n = 31;
            break;
        case 2:
        {
            if ((i % 4 == 0 && i % 100 != 0) || i % 400 == 0) //if (i % 4 == 0) 修改
            {
                n = 29;
            } 
            else
            {
                n = 28;
            }
        }
        break;
        case 3: n = 31;
            break;
        case 4: n = 30;
            break;
        case 5: n = 31;
            break;
        case 6: n = 30;
            break;
        case 7: n = 31;
            break;
        case 8: n = 31;
            break;
        case 9: n = 30;
            break;
        case 10: n = 31;
            break;
        case 11: n = 30;
            break;
        case 12: n = 31;
            break;
        default:
            n = 0;      //修改 
            printf("ERROR\n");
        }
        if(n)           //修改 
            printf("%d\n", n);
    }
    return 0;
}

那是0不是O好吗？是那个n的值