这是ac的代码

#include <bits/stdc++.h>
using namespace std;
const int N = 50010;
int p[N];
int n,m;
int find(int x)
{
    if (p[x] != x)p[x] = find(p[x]);
    return p[x];
}
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    int t = 1;
    while (cin >> n >> m , n && m)
    {
        int res = n;
        for (int i = 1;i <= n;i ++)p[i] = i;
        while (m --)
        {
            int a,b;
            // scanf("%d%d",&a,&b);
            cin >> a >> b;
            int px = find(a),py = find(b);
            if (px == py)continue;
            else 
            {
                p[find(a)] = find(b);
                res --;
            }
        }
        printf("Case %d: %d\n",t,res);
        t ++;
    }
    return 0;
}

但是我在主函数中的第二层while循环里面将a,b的输入改为scanf就会re