VS c++ 函数重复定义问题

cryptography.h

#pragma once

void getVerCode();

cryptography.cpp

#include "cryptography.h"
#include<iostream>
#include<cstdlib>
#include<time.h> 
#include<math.h>

using namespace std;

void getVerCode()
{
    int _new;
    int N = 99;
    int _low = 0;
    int _flag = 0;
    int verCode[256]={}, _verCode[6]={};
    for (int i = 1; i <= N; i++)
    {
        int flag = (rand() % 2 == 0) ? 1 : 0;
        _low = _low ^ (flag << (i - 1));
    }
    for (int i = 1; i < 256; i++)
    {
        verCode[i] = (_low & 1);
        _new = _low & 1 ^ ((_low >> 4) & 1);
        _low = _low >> 1 ^ (_new << 4);
    }
    for (int i = 255; i > 0; i -= 5)
    {
        int x;
        x = verCode[i] + verCode[i - 1] * 2 + verCode[i - 2] * 4 + verCode[i - 3] * 8;
        if (x < 10)
        {
            _verCode[_flag] = x;
            _flag++;
        }
        if (_flag >= 5)
        {
            break;
        }
    }
    cout << "验证码为：";
    for (int i = 0; i < 6; i++)
    {
        cout << _verCode[i];
    }
}

main.cpp

#include"cryptography.cpp"
int main()
{
    srand((unsigned)time(NULL));
    int flag;
    for (int i = 0; i < 10; i++)
    {
        getVerCode();
        cout << endl;
    }
    cin >> flag;
    return 0;
}

调试显示：
1>main.obj : error LNK2005: "void __cdecl getVerCode(void)" (?getVerCode@@YAXXZ) 已经在 cryptography.obj 中定义
1>C:\Users\Administrator\source\repos\WorkPacketForC++Course\x64\Debug\WorkPacketForC++Course.exe : fatal error LNK1169: 找到一个或多个多重定义的符号
1>已完成生成项目“WorkPacketForC++Course.vcxproj”的操作 - 失败。

请问如何解决？

main.cpp 中#include "cryptography.h"