C语言一个小小的问题，望解答

Question

请问下面代码中为什么多一个输出语句程序是对的，去掉就不可以运行了呢？
一定和输入缓存区有关系么？加一个fflush也可以，就是不知道为什么？？？

 #include <stdio.h>
#include <string.h>
#include<stdlib.h>
long int sum,tsum,tnum;
struct word
{
    char str[105];
    int num;
} A[2][10005];
void chuli(char s[],int k)
{
    int i,j,flag=0;
    for(i=0; i<=sum; i++)
    {
        if(strcmp(A[k][i].str,s)==0)
        {
            A[k][i].num++;
            flag=1;
            sum++;
        }
    }
    if(flag==0)
    {
        for(j=0; j<105; j++)
            A[k][sum].str[j]=s[j];
        A[k][sum].num++;
        sum++;
        if(k==0)tnum++;
        else tsum++;
    }
}
void paixu2()
{
    int i,j;
    char c[105];
    struct word a;
    for(i=0; i<sum; i++)
    {
        for(j=i+1; j<sum; j++)
            if(A[1][i].num<A[1][j].num)
            {
                a=A[1][j];
                A[1][j]=A[1][i];
                A[1][i]=a;
            }
            else if(A[1][i].num==A[1][j].num&&strcmp(A[1][i].str,A[1][j].str)>0)
            {
                strcpy(c,A[1][j].str);
                strcpy(A[1][j].str,A[1][i].str);
                strcpy(A[1][i].str,c);
            }
    }
}
void chong()
{
    int i,j;
    for(i=0; i<tsum; i++)
    {
        for(j=0; j<tnum; j++)
        {
            if(strcmp(A[0][j].str,A[1][i].str)==0)A[1][i].num=0;
        }
    }
}
void input2(int k)
{
    char ch,s[105]= {'\0'};
    int i;
    sum=0;
    for(i=0; i<10005; i++)
        A[k][i].num=0;
    scanf("%*s%*c");
    while(ch!=-1&&ch!='<')
    {
        for(i=0; i<105; i++)s[i]='\0';
        ch=getchar();
        if(ch>='A'&&ch<='Z')ch+=32;
        if((65<=ch&&ch<=90)||(ch>=97&&ch<=122))
        {
            for(i=0;; i++)
            {
                s[i]=ch;
                ch=getchar();
                if(ch>='A'&&ch<='Z')ch+=32;
                if((65<=ch&&ch<=90)||(ch>=97&&ch<=122))continue;
                else break;
            }
            chuli(s,k);
        }
    }
    scanf("%*s%*c");
    if(k==1)
    {
        chong();
        paixu2();
    }
}
int main()
{
    int n,i;
    scanf("%d%*c",&n);
    while(n--)
    {
        for(i=0; i<10005; i++)
            for(int k=0; k<2; k++)
                memset(A[k][i].str,'\0',sizeof(A[k][i].str));
        tnum=0,tsum=0,sum=0;
        input2(0);
                //fflush(stdin);
        printf("****\n");/*********这个输出一定要有，并且不可以什么也不输出，不懂为什么*/
        input2(1);
        for(i=0; i<tsum&&i<10; i++)
        {
            if(A[1][i].num==0)continue;
            printf("%s\n",A[1][i].str);
        }
        //fflush(stdin);
        if(n!=0)printf("\n");
    }
    return 0;
}

********下面是测试数据***********

* **** Sample Input****
2
<oldwords>
how aRe you
</oldwords>
<article>
--How old are you?
--Twenty.
</article>
<oldwords>
google cn huluobo net i
</oldwords>
<article>
文章内容：
I love google,dropbox,firefox very much.
Everyday I open my computer , open firefox , and enjoy surfing on the inter-
net.
But these days it's strange that searching "huluobo" is unavail-
able.
What's wrong with "huluobo"?
</article>


* ******Sample Output******
old
twenty

firefox
open
s
able
and
but
computer
days
dropbox
enjoy

Answer 1

 void input2(int k)
{
    char ch,s[105]= {'\0'};
    int i;
    sum=0;
    for(i=0; i<10005; i++)
        A[k][i].num=0;
    scanf("%*s%*c");
    while(ch!=-1&&ch!='<') // ch未赋值