我不太明白为什么我得到这个关于向量的错误

我的程序接受两个输入文件，其中一个是命令列表。文件的每一行都是一个新的命令，所以我想把这个文件解析成一个数组。我被告知使用一个动态增长的向量，这样就不需要一个函数来计算文件中的行数，然后使用这些数据来创建一个数组。

下面是我现在的程序:

#include<iostream>
#include<string>
#include<fstream>
#include<vector>
using namespace std;

//Prototypes
int parseLines(ifstream& countfile);

vector<string> parseLines(ifstream& countfile)
//counts number of lines in file passed to function
{
   string line;
   vector<string> lines;
   int numberOfLines;
   //reads through each line until end of file putting each line in a sperate entry of the vector
   while(getline(countfile, line))
   {
       lines.push_back(line);
   }
   return lines;
}

int main (int argc, char* argv[])
{
        int i;
    if(argc != 3) cout << "Usage: calendar.out datafile inputfile";
    //Create input streams to both files
    ifstream apptsfp;
    ifstream inputfp;
    //Open streams to both files
    apptsfp.open(argv[1]);
    inputfp.open(argv[2]);
    if(!inputfp.is_open())
    {
        cerr << "failed to open input filen";
        return 1;
    }
        vector<string> inputVector;
        vector<string> apptsVector;
    inputVector = parseLines(inputfp);
        for(i=0; i<= inputVector.size(); i++)
        {
        cout << "Input " << i << ": " << inputVector[i] << endl;
        }
    return 0;
}

和我得到这个长错误当我编译，我不太明白它:

$ g++ calendar.cpp
calendar.cpp: In function ‘std::vector<std::basic_string<char> > parseLines(std::ifstream&)’:
calendar.cpp:17:46: error: new declaration ‘std::vector<std::basic_string<char> > parseLines(std::ifstream&)’
calendar.cpp:14:5: error: ambiguates old declaration ‘int parseLines(std::ifstream&)’
calendar.cpp: In function ‘int main(int, char**)’:
calendar.cpp:58:37: error: no match for ‘operator=’ in ‘inputVector = parseLines((* & inputfp))’
calendar.cpp:58:37: note: candidate is:
In file included from /usr/include/c++/4.7/vector:70:0,
                 from calendar.cpp:9:
/usr/include/c++/4.7/bits/vector.tcc:161:5: note: std::vector<_Tp, _Alloc>& std::vector<_Tp, _Alloc>::operator=(const std::vector<_Tp, _Alloc>&) [with _Tp = std::basic_string<char>; _Alloc = std::allocator<std::basic_string<char> >]
/usr/include/c++/4.7/bits/vector.tcc:161:5: note:   no known conversion for argument 1 from ‘int’ to ‘const std::vector<std::basic_string<char> >&’

我觉得我不太懂如何使用向量