Solution for my birthday crackme part 1 ;)

birthdayp1.cpp

#include "stdafx.h"
#include <string>
#include <iostream>
#include <fstream>

using namespace std;

unsigned int checksum(unsigned char string[]) {
	unsigned int var;

	unsigned int eax;
	unsigned int ecx;
	unsigned int esi;

	unsigned char value1;
	unsigned char value2;
	unsigned char value3;

	unsigned int * pointer1;
	unsigned int * pointer2;
	unsigned int * pointer3;

	int a;

	/* pointer1 should point to the second byte of var */

	pointer1 = &var;
	a = (int)pointer1;
	a = a + 1;
	pointer1 = (unsigned int *)a;

	/* pointer2 should point to the first byte of eax */

	pointer2 = &eax;

	/* pointer3 should point to the second byte of eax */

	pointer3 = &eax;
	a = (int)pointer3;
	a = a + 1;
	pointer3 = (unsigned int *)a;


	esi = 0;
	eax = 0;
	var = 0;
	ecx = 4;

	while (ecx != 0)
	{

		/* xor byte ptr [var+1], ah */

		value1 = eax >> 8;
		value2 = var >> 8;
		value3 = value1 ^ value2;
		*pointer1 = value3;

		/* lodsw */

		* pointer2 = string[esi];
		*pointer3 = string[esi + 1];
		esi = esi + 2;

		/* dec ecx */

		ecx--;

		/* add  [var], eax */

		var = var + eax;
	}
	return var;
}

int _tmain(int argc, _TCHAR* argv[])
{
	string line;
	ifstream myfile("my1.txt");
	if (myfile.is_open())
	{
		while (getline(myfile, line)) {
			unsigned int var = checksum((unsigned char *) line.c_str());
			if (var == 0x39a)
				cout << line.c_str() << endl;
		}
		myfile.close();
	}
	else cout << "Unable to open file";
	
	return 0;
}