I created a simple win32 console application just for this testing purpose. Lately the idea of reverse engineering has intrigued me I know isn't easy to do it, but I also know that it would more or less depend on what you are reversing, obviously the smaller the application the easier it should be or at least that is my assumption on that.

Here is my sample code:

#include <iostream>

using namespace std;

struct CVar
{
int num;
};

int main()
{
CVar cvar;
cvar.num = 250;

int choice = 0;
bool isRunning = true;
while(isRunning)
{
cout << endl;
cout << "MENU OPTIONS\n";
cout << "1 - Increment\n";
cout << "2 - Deincrement\n";
cout << "3 - Display number\n";
cout << "9 - EXIT\n";
cout << "Enter choice: ";
cin >> choice;
cout << endl;
switch(choice)
{
case 1:
cvar.num++;
break;
case 2:
cvar.num--;
break;
case 3:
cout << "\nCVar num: " << cvar.num << endl;
break;
case 9:
isRunning = false;
break;
}
}
}


After running my .exe file in IDA I see that say I want to change the value of player.posY externally and I don't mean just increment it by using switch cases. Initially it is set to 250, but now I want it to be 450 or 1c2 (hex). I see the following in my disassembly for this variable.


mov [ebp+var_8], 0FAh //Where it is declared


than I find that var_8 = dword ptr -8

when you increment via the switch case you see this asm code

mov eax, [ebp+var_8]
add eax, 1 //since 1 is the hex value for 1
move [ebp+var_8], eax


I have taken an ASM class about a year ago, so a little refresher would probably be required, but how would I go about creating an external program to change this value without doing anything via switch case? I did this little program because I figured it would be a good small application to learn on. Any idea or helpful pointers would be greatly appreciated. Thank you.