求助！！

样例对了但错了！！

#include<bits/stdc++.h>
#define int long long
using namespace std;
int n;
string s1,s2;
char a;
signed main()
{
	cin>>n;
	for(int j=1;j<=n;j++)
	{
		cin>>s1>>s2;
		a=s1[0];
		s1[0]=s2[0];
		s2[0]=a;
		for(int i=0;i<s1.size();i++)
		{
			cout<<s1[i];
		}
		cout<<" ";
		for(int i=0;i<s2.size();i++)
		{
			cout<<s2[i];
		}
		cout<<endl;
	}
	return 0;
}