Question

The game of Nim: This is a well-known game with a number of variants. The following variant has an interesting winning strategy. Two players alternately take marbles from a pile. In each move, a player chooses how many marbles to take. The player must take at least one but at most half of the marbles. Then the other player takes a turn. The player who takes the last marble loses.

Write a C program in which the computer plays against a human opponent. Generate a random integer between 10 and 100 to denote the initial size of the pile. Generate a random integer between 0 and 1 to decide whether the computer or the human takes the first turn. Generate a random integer between 0 and 1 to decide whether the computer plays smart or stupid. In stupid mode the computer simply takes a random legal value (between 1 and n / 2) from the pile whenever it has a turn. In smart mode the computer takes off enough marbles to make the size of the pile a power of two minus 1—that is, 3, 7, 15, 31, or 63. That is always a legal move, except when the size of the pile is currently one less than a power of two. In that case, the computer makes a random legal move.

You will note that the computer cannot be beaten in smart mode when it has the first move, unless the pile size happens to be 15, 31, or 63. Of course, a human player who has the first turn and knows the winning strategy can win against the computer.

Note: Loops can be written using while, for and do-while statements. For this question, you can’t use same loop statement twice (For example: if you have to use nested loop, you can’t use for loop inside a for loop. It has to be for loop inside a while or vice versa)!

This is what I have so far.....

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int humanplays(int pile)
{
   printf("How many? ");
   int take;
   scanf("%d", &take);

   return pile - take;
}
//In stupid mode the computer simply takes a random legal value (between 1 and n / 2)
//from the pile whenever it has a turn.
int computerplays(int pile, int smart)
{
   if(smart)
   {

   }
   else
   {
       int take = rand() % (pile/2) + 1;
       printf("Computer stupidly takes %d\n", take);
       return pile - take;
   }
}

int main()
{
   srand(time(NULL));
   int pile = rand() % 91 + 10;
//   printf("got %d\n", pile);

//zero is computer 1 is human
   int next = rand() % 2;
//decides whether computer is smart(1) or stupid(0)
   int smart =rand() % 2;
   smart = 0;

   printf("%d in pile, next = %d smart = %d\n", pile, next, smart);

   while(pile > 0)
   {
       pile = humanplays(pile);
       printf("%d remain\n", pile);
       if(pile == 1)
       {
           printf("Human wins!");
           break;
       }
       pile = computerplays(pile, smart);
       printf("%d remain\n", pile);
       if(pile == 1)
       {
           printf("Computer wins!");
           break;
       }
   }
}

Answer 1

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int main()
{
srand(time(NULL));
// Generating the random size, smartness and turn
int pile = rand()%91 + 10;
int next = rand()%2;
int smart = rand()%2;
//print the smartness
if(smart==1)
printf("Computer is smart");
else
printf("Computer is stupid");
while(pile > 1)
{
// Print the size
printf(" The size of the pile is %d ", pile);
if(next == 0)
{
int value = 0;
// Take input till a valid value is entered
do
{
printf(" Its your turn. Enter a legal value between 1 and %d ", pile/2);
scanf("%d", &value);
} while (value <= 0 || value > pile/2);
pile = pile - value;
next = 1;
}
else
{
// The computer's turn
printf(" Its computer's turn! ");
if(smart == 0)
{
// Select random number of withdrawl
int value = rand()%(pile/2) + 1;
printf(" The computer has taken out %d marbles. ", value);
pile = pile - value;
}
else
{
int power = 1;
// In order to find out which is the largest power of 2 that can be achieved
for(power = 2; power < pile + 1; power = power*2)
{
if(pile <= power - 1)
{
break;
}
}
// If already at a stage of power of 2 - 1
if(pile == power - 1)
{
int value = rand()%(pile/2) + 1;
printf(" The computer has taken out %d marbles. ", value);
pile = pile - value;
}
// Achieve the required value
else
{
power = power/2;
int value = pile - (power - 1);
printf(" The computer has taken out %d marbles. ", value);
pile = pile - value;
}
}
next = 0;
}
}
if(next == 0)
printf(" Computer wins ");
else
printf(" You win ");
return 0;
}