又是文件中字符串显示有关问题（比较棘手）

又是文件中字符串显示问题（比较棘手）
e:\test1文件内容如下：
Begin:
this   is   the   100th   line;
not   the   99th   line;
this   is   the   100th   line;
end;

Begin:
this   is   the   101th   line;
not   the   100th   line;
this   is   the   101th   line;
end;

Begin:
this   is   the   102th   line;
not   the   101th   line;
this   is   the   102th   line;
end;
要求从键盘录入一个字符如“101”，显示
Begin:
this   is   the   101th   line;
not   the   100th   line;
this   is   the   101th   line;
end;  
而不能显示
Begin:
this   is   the   102th   line;
not   the   101th   line;
this   is   the   102th   line;
end;
求完整程序，万分感谢，100分全奖励第一个给出能运行的答案的人！

------解决方案--------------------
#include <fstream>
#include <iostream>
#include <cstdlib>

using namespace std;

//#include <sys\stat.h>
//#include <string.h>
//#include <time.h>
//#include <stdio.h>
//#include <stdlib.h>

int main(int argc, char *argv[])
{
int num;
cout < < "Input num: ";
cin> > num;
char tmp[40];
sprintf(tmp, "this is the %dth line; ", num); //构造比较串

ifstream infile( "test.txt ");
string line;
while(!infile.eof())
{
getline(infile, line);
if(line == "Begin: ") //开始串匹配
{
getline(infile, line);
if(line==tmp) //匹配比较串
{
cout < < "Begin: " < <endl;
cout < <line < <endl;
while(line != "end; ") //循环读取输出，直到 end; 结束
{
getline(infile, line);
cout < <line < <endl;
}
break;
}
}
}

system( "pause ");
return 0;
}


test.txt文件内容（当前目录下）：
Begin:
this is the 100th line;
not the 99th line;
this is the 100th line;
end;

Begin:
this is the 101th line;
not the 100th line;
this is the 101th line;
end;

Begin:
this is the 102th line;
not the 101th line;
this is the 102th line;
end;
------解决方案--------------------
#include <iostream>
#include <fstream>
#include <string>

using namespace std;


void ReadBlock(ifstream& infile,
string const& begin,
string const& end,
string& block)
{
string line;
bool foundBegin = false;
bool foundEnd = false;
while (infile && !infile.eof()) {
getline(infile, line);
string::size_type idxSub = string::npos;
if ( !foundBegin) idxSub = line.find(begin, 0);
if ( idxSub!=string::npos) {
foundBegin = true;
}
if ( foundBegin) {
block.append(line);
block.append( "\n ");
idxSub = line.find(end, 0);
if (idxSub != string::npos) {