This article is from solution of Let Us C by Yashwant Kanetkar. I also posted many another articles regarding solutions of Let Us C. If you have any problem regarding solution then give comment, I will surely reply your question.
Q. Write a program for a matchstick game being played between the computer and a user. Your program should ensure that the computer always wins. Rules for the game are as follows.
1.There are total 21 matchsticks.
2.You can select either 1, 2, 3 or 4 matchsticks at a time.
3.After the person picks Computer does its picking.
4.Whoever is forced to pick up the last matchstick loses the game.
Ans.
#include<stdio.h>
#include<conio.h>
void main()
{
clrscr();
int usr=0,i,comp=0,rmnf,rmn=21;
printf("Rules For The Game:\n");
printf("1.There are total 21 matchsticks.\n2.You can select either 1, 2, 3 or 4 matchsticks at a time.\n3.After the person picks Computer does its picking\n4.Whoever is forced to pick up the last matchstick loses the game.");
do
{
rmn=rmn-comp;
printf("\n\nRemaining Matchsticks: %d",rmn);
printf("\nEnter number of matchsticks you pick: ");
scanf("%d",&usr);
clrscr();
if((usr<=4 && rmn>=6) || (usr==1 && rmn<=6))
{
rmn=rmn-usr;
if(rmn!=0)
{
comp=5-usr;
printf("\nYou have selected %d Matchsticks",usr);
printf("\nComputer Selected %d Matchsticks",comp);
}
else if(rmn==0)
{
printf("\nRemaining Matchsticks Are %d",rmn);
printf("\nYou Picked Last Matchstick");
printf("\nYOU LOST THE GAME");
break;
}
}
else
{
printf("\nPlease Enter a valid choice i.e. 1 2 3 or 4");
comp=0;
}
}while(1);
getch();
}
The logic behind the program is:
There are total 21 matchsticks and who forced to select last one is lost and we wanted to make a program in which computer always win so the last matchstick should be selected by the user. so we wanted that whenever the last selection of user is come into the picture at that time there should be only 1 matchstick remaining and there is a rule that user or computer can select at most 4 matchsticks at a time so for making force on user to select last matchstick whenever the user's second last (last is the turn when there is only 1 matchstick remaining) selection turn is arrived at that time there should be 6 matchsticks remaining so user selects any number of match sticks from 1,2,3 or 4 after that computer selects (5-number of matchsticks selected by the user ) so at the selection turn of user there is only one matchstick is remaining. This last step is possible only if at each turn the sum of selected matchsticks by computer and selected matchsticks by user is 5. so we tell the computer via program that after each time the selection done by user computer should select (5-number of matchsticks selected by the user) matchsticks so at each turn there should 5 matchsticks less than the previous turn.
So the whole program is run in following fashion
At 1st turn
Remaining Matchsticks :- 21
User selects 1,2,3 or 4 matchsticks
Computer Selects 5-number of matchsticks selected by the user
At 2nd turn
Remaining Matchsticks :- 16
User selects 1,2,3 or 4 matchsticks
Computer Selects 5-number of matchsticks selected by the user
At 3rd turn
Remaining Matchsticks :- 11
User selects 1,2,3 or 4 matchsticks
Computer Selects 5-number of matchsticks selected by the user
At 4th turn
Remaining Matchsticks :- 6
User selects 1,2,3 or 4 matchsticks
Computer Selects 5-number of matchsticks selected by the user
At 5th turn
Remaining Matchsticks :- 1
User selects 1 matchstick because only 1 matchstick is remaining
