Modifying 13 stones game to force computer to make specific first move

[ALi Shaikh]

I already did the game once and it works but now I need to change it to add a function that will make the computer take player 1 turn and always win.
heres the original

#include<iostream.h>
 
void main()
{
    int nums, // stones left
        nump,   // Number of stones picked up by player
        player;
              // Player identifier (1 or 2)
 
 
    cout << endl; 
    cout << "You have before you a pile of 13 stones. "
         << "Players 1 and 2 alternate" << endl;
    cout << "picking from 1 to 3 stones off the pile. "
         << "The last player to pick up " << endl;
    cout << "a stone is the winner. Good luck."  << endl;
    cout << endl;
 
 
    nums = 13;
    player = 1;
 
    while ( nums>0 )   // While there is a stone remaining
    {
 
       cout<<"Pick stones player number "<<player<<" : "; // Prompt player to pick up 1-3 stones.
       cin>>nump;
 
    if( nump>0&&nump<4)
     {
      nums-=nump;
      if (nums<1)
      {
 
    cout << "No stones left -- "
         << "player " << player << " is the winner!" << endl;
         }
      cout<<nums<<" stones are left\n";
       player++;
         if(player>2)
    {
      player=1; 
     }  
 
     }
     else
     {
     cout<<"Cheata\n";
     }
 
     // If move is legal, then subtract the number of stones played
        // and change players (if a win has not occurred).
 
 
 
 
    }
 
 
 
}
 

How do I do it

[sicarie]

So there are two parts to this - the function declaration, and the implementation.

Do you know how to create a function "prototype"?

From there, you need to define your algorithm to make the computer move the way you want it, and then (I'm guessing) turn it over to the user.

[RRick]

You first will need an algorithm (basically a generalized idea) that the computer will use to figure out how many stones to pick. Once you figure that out, you write the routine to implement the algorithm.

The trick here is to realize that whoever gets to pick with 4 stones in a pile looses. To win, you want 3 * n + 1 stones (where n=1,2,3,...) MORE than 4 stones in the pile. Once there are less that 4 stones, you take the rest and win.

You can write an algorithm that calculates the the number to remove from a given value from the above idea. Since you don't have many rocks to work with, you can create a table (from the above algor) that tells the computer how many rocks should be left after it removes some rocks. In this case, you find the largest number in the table that is less than the current number