Coding tic tac toe in C

Question

I'm coding a game of tic tac toe in C. Here's the logic. The User goes first, selects a slot. The positions of the slot are calculated using simple formulae. Then the selected slot is filled. Next, the computer selects a slot, randomly. For this, i've used the rand() function, in stdlib.h. Initially, all elements of the 3x3 matrix are set at 0. My problem is, even if all the other elements are 0, and the user selects slot 5 or slot 9, the user wins. Same thing for the comp also. Here's my code-

#include<stdio.h>
#include<stdlib.h>
int check(int[][3]);
void print(int[][3]);
main()
{
 int i,j,match[3][3]={0},posx,posy,comp_posx,comp_posy,fill=0,slot,user_score=0,comp_score=0;
 char ch;
 srand(time(NULL));
 do
 {
  while(fill<9)
  {
   printf("\nEnter the slot you want to fill.\n");
   scanf("%d",&slot);
   if (slot > 9)
   {
    printf("Error!\nSlot value cannot exceed 9.\n");
    continue;
   }
   else if( slot >= 1&&slot <=3)
   {
    posx=0;
    posy=slot-1;
   }
   else if (slot >= 4 && slot <= 6)
   {
    posx=1;
    posy=slot-4;
   }
   else
   {
    posx=2;
    posy=slot-7;
   }
   if (match[posx][posy] == 0)
   {
    match[posx][posy]=1;
    fill++;
    check(match);
    if(check(match)==1)
    {
     printf("The user wins!\n");
     user_score++;
     print(match);
     break;
    }
    else if(check(match)==-1)
    {
     printf("The computer wins!\n");
     comp_score++;
     print(match);
    }
    else
    {
     if(fill==9)
     {
      printf("It's a draw!\n");
      print(match);
      break;
     }
     else
     {
      printf(" ");
     }
    }
   }
   else
   {
    printf("Sorry! This slot is already filled.\nPlease pick another slot.\n");
    continue;
   }
   label:
   comp_posx=rand()%3;
   comp_posy=rand()%3;
   if(match[comp_posx][comp_posy]==0)
   {
    match[comp_posx][comp_posy]=-1;
    fill++;
    check(match);
    if (check(match)==1)
    {
     printf("The user wins!\n");
     user_score++;
     print(match);
     break;
    }
    else if(check(match)==-1)
    {
     printf("The computer wins!\n");
     comp_score++;
     print(match);
     break;
    }
    else
    {
     if (fill==9)
     {
      printf("It's a draw!\n");
      print(match);
      break;
     }
     else
     {
      printf(" ");
     }
    }
   }
   else
   goto label;
   for(i=0;i<3;i++)
   {
    printf("\n");
    for(j=0;j<3;j++)
    {
    printf("%d\t",match[i][j]);
    }
   }
  }
  for(i=0;i<3;i++)
  {
   for(j=0;j<3;j++)
   {
    match[i][j]=0;
   }
  }
  printf("Continue? Y/N\n");
  scanf("%c %c",&ch,&ch);
 }
 while(ch=='y'||ch=='Y');
 printf("FINAL SCORES>>\nUser=%d\nComputer=%d\n",user_score,comp_score);
}
int check(int match[][3])
{
 int i,j;
 if( match[2][0]==match[1][1] && match[1][1]==match[0][2] )
 {
  if (match[0][2]==1)
  return 1;
  else if (match[0][2]==-1)
  return -1;
  else
  printf(" ");
 }
 for(i=0;i<3;i++)
 {
  if (match[i][0]==match[i][1]&&match[i][1]==match[i][2])
  {
   if(match[i][1]==1)
   return 1;
   else if(match[i][1]==-1)
   return -1;
   else
   continue;
  }
 }
 for(j=0;j<3;j++)
 {
  if(match[0][j]==match[1][j]&&match[0][j]==match[2][j])
  {
   if (match[0][j]==1)
   return 1;
   else if(match[0][j]==-1)
   return -1;
   else
   continue;
  }
 }
 for (i=0;i<1;i++)
 {
  if(match[i][i]==match[i+1][i+1]&&match[i][i]==match[i+2][i+2])
  {
   if (match[i][i]==1)
   return 1;
   else if (match[i][i]==-1)       return -1;
  else continue;
  }
 }
}
 void print(int match[][3])
 {
  int i,j;
  for(i=0;i<3;i++)
  {
   printf("\n");
   for(j=0;j<3;j++)
   {
    printf("%d\t",match[i][j]);
   }
  }
 }

Can You suggest changes in the code, so that i won't have those problems?

Answer 1

This code has a lot of mess, but the reason for your problem is that you don't return value (or, in other words, return garbage value) from check if nobody wins. Add the line return 0; at the end of check.