这些换行有的是 \n 有的是 \r，一定要两个都判一下：

60 分：

#include <bits/stdc++.h>
using namespace std;

vector <string> v;
string a, b;

int f = 1;
string read()
{
	string str;
	char c;
	while(c != ' ')
	{
		c = getchar();
		if(c == '\n')
		{
			f = 0;
			break;
		}
		if(c != ' ')
			str += c;
	}
	return str;
}

int main()
{
	while(1)
	{
		string str;
		str = read();
		v.push_back(str);
		if(f == 0)
			break;
	}
	cin >> a >> b;
	for(int i = 0; i < v.size(); i = i + 1)
	{
		if(v[i] == a)
			cout << b;
		else
			cout << v[i];
		cout << " ";
	}
	return 0;
}

100 分：

#include <bits/stdc++.h>
using namespace std;

vector <string> v;
string a, b;

int f = 1;
string read()
{
	string str;
	char c;
	while(c != ' ')
	{
		c = getchar();
		if(c == '\n' || c == '\r')
		{
			f = 0;
			break;
		}
		if(c != ' ')
			str += c;
	}
	return str;
}

int main()
{
	while(1)
	{
		string str;
		str = read();
		v.push_back(str);
		if(f == 0)
			break;
	}
	cin >> a >> b;
	for(int i = 0; i < v.size(); i = i + 1)
	{
		if(v[i] == a)
			cout << b;
		else
			cout << v[i];
		cout << " ";
	}
	return 0;
}