这个代码为什么只有第一个文件输出正确，而其他的.out文件输出都错误（为0）？

#include<bits/stdc++.h>
using namespace std;
const long long M=1e8,N=1e7+555555,INFN=10;
long long n;
string filename[114514]=
{
	"a1", //1
        "a2", //2
        "a3", //3
        "a4", //4
        "a5", //5
        "a6", //6
        "a7", //7
        "a8", //8
        "a9", //9
        "a10", //10
        "a11", //11
        "a12", //12
        "a13", //13
        "a14", //14
        "a15", //15
        "a16", //16
        "a17", //17
        "a18", //18
        "a19", //19
        "a20", //20
        "a21", //21
        "a22", //22
        "a23", //23
        "a24", //24
        "a25", //25

};
long long rand(long long x)
{
	return rand()%x;
}
long long rand(long long a,long long b)
{
	if(b>a) swap(a,b);
	return rand(a-b)+b;
}
void tianx()
{
	printf("%d",rand(100));
}
void answer()
{
	int n;
	cin>>n;
	printf("%d\n",n);
}
int main()
{
	srand(time(0));
	for(int i=0;i<INFN;i++)
	{
		freopen((filename[i]+".in").c_str(),"w",stdout);
		tianx();
		fclose(stdout);
		freopen((filename[i]+".in").c_str(),"r",stdin);
		freopen((filename[i]+".out").c_str(),"w",stdout);
		answer();
		fclose(stdin);
        fclose(stdout);
	}
}
/*
freopen("a.in","r",stdin);
freopen("a.out","w",stdout);

freopen("a.in","w",stdout);
*/

求求了: (