main函数部分如下:

int main()
{
	getline(cin, str);
	cin >> i >> j;
	str =  " " + str + " ";
	i =  " " + i + " ";
	j =  " " + j + " ";
	while(str.find(i, pos) != str.npos){
		pos = str.find(i, pos);
		str.replace(pos, i.size(), j);
		pos ++;
	}
	str.erase(0, 1);
	cout << str << endl;
	return 0;
}