tic tac toe in Dev-C++ 4.9.9.2

Hi I wrote a tic tac toe game that uses 2 human players. However, I want to re-write the game where it only need 1 human and the second player is the computer. The only problem is I don't know how to do that. If someone has some good tips, link, or anything that can help me would great. Thanks.

Here is my two player version

Code:

#include "simpio.h"
#include <stdio.h>

char matrix[3][3];//={0};

void board(void);
int main()
{
int m,n;
char ch='y';
char x='X';
char o='O';
char again;
while(ch=='Y'||ch=='y'){
for (m=0;m<3;m++)for (n=0;n<3;n++)matrix[m][n]= '\0';
int i,j,sum=0;
while ( sum < 10){
if (sum == 0) board();
printf("Player 1 is 'X': choose the row and column");
printf("\nRow : ");
i=GetInteger();
printf("\nColumn : ");
j=GetInteger();
for (; i>3 || i<1 || j>3 || j<1 ||('X'==matrix[i-1][j-1]||'O'==matrix[i-1][j-1]);) 
{
    printf("Sorry, but you gotta choose another place.\n");
    printf("row : ");
    i=GetInteger();
    printf("column : ");
    j=GetInteger();
    }
matrix[i-1][j-1]='X';
sum++;
board();

//check if wins
if (matrix[0][0]=='X' && matrix[0][0]==matrix[1][1] && matrix[1][1]==matrix[2][2]) {printf("Player 1 wins");break;}
if (matrix[2][0]=='X' && matrix[2][0]==matrix[1][1] && matrix[1][1]==matrix[0][2]) {printf("Player 1 wins");break;}
if (matrix[0][0]=='X' && matrix[0][0]==matrix[1][0] && matrix[1][0]==matrix[2][0]) {printf("Player 1 wins");break;}
if (matrix[0][1]=='X' && matrix[0][1]==matrix[1][1] && matrix[1][1]==matrix[2][1]) {printf("Player 1 wins");break;}
if (matrix[0][2]=='X' && matrix[0][2]==matrix[1][2] && matrix[1][2]==matrix[2][2]) {printf("Player 1 wins");break;}
if (matrix[0][0]=='X' && matrix[0][0]==matrix[0][1] && matrix[0][1]==matrix[0][2]) {printf("Player 1 wins");break;}
if (matrix[1][0]=='X' && matrix[1][0]==matrix[1][1] && matrix[1][1]==matrix[1][2]) {printf("Player 1 wins");break;}
if (matrix[2][0]=='X' && matrix[2][0]==matrix[2][1] && matrix[2][1]==matrix[2][2]) {printf("Player 1 wins");break;}

if (sum == 9){printf("The game is over and no one wins"); break;} //sum=9 because there are only 9 boxes in the game
//player 2's turn

printf("Player 2 is 'O': choose the row and column");
printf("Row : ");
i=GetInteger();
printf("Column : ");
j=GetInteger();
for (;i>3 || i<1 || j>3 || j<1 ||('X'==matrix[i-1][j-1]||'O'==matrix[i-1][j-1]);) 
{
printf("Sorry, but you gotta choose another place.\n");printf("row : ");i=GetInteger();printf("column : ");j=GetInteger();}
matrix[i-1][j-1]=o;
sum++;
//the play box
board();
//check if wins
if (matrix[0][0]=='O' && matrix[0][0]==matrix[1][1] && matrix[1][1]==matrix[2][2]) {printf("Player 2 wins");break;}
if (matrix[2][0]=='O' && matrix[2][0]==matrix[1][1] && matrix[1][1]==matrix[0][2]) {printf("Player 2 wins");break;}
if (matrix[0][0]=='O' && matrix[0][0]==matrix[1][0] && matrix[1][0]==matrix[2][0]) {printf("Player 2 wins");break;}
if (matrix[0][1]=='O' && matrix[0][1]==matrix[1][1] && matrix[1][1]==matrix[2][1]) {printf("Player 2 wins");break;}
if (matrix[0][2]=='O' && matrix[0][2]==matrix[1][2] && matrix[1][2]==matrix[2][2]) {printf("Player 2 wins");break;}
if (matrix[0][0]=='O' && matrix[0][0]==matrix[0][1] && matrix[0][1]==matrix[0][2]) {printf("Player 2 wins");break;}
if (matrix[1][0]=='O' && matrix[1][0]==matrix[1][1] && matrix[1][1]==matrix[1][2]) {printf("Player 2 wins");break;}
if (matrix[2][0]=='O' && matrix[2][0]==matrix[2][1] && matrix[2][1]==matrix[2][2]) {printf("Player 2 wins");break;}

}
printf("\nWould you like to play again??? (Y - N)\n");
ch=getchar();
}
      getchar();
      return 0;
}
void board(void)
{
//the play box
printf("\n\t\t                1   2   3\n");
printf("\t\t             1  %c | %c | %c\n", matrix[0][0],matrix[0][1],matrix[0][2]); 
printf("\t\t               ---|---|---\n"); 
printf("\t\t             2  %c | %c | %c\n", matrix[1][0],matrix[1][1],matrix[1][2]);
printf("\t\t               ---|---|---\n");         
printf("\t\t             3  %c | %c | %c\n", matrix[2][0],matrix[2][1],matrix[2][2]);
}

Any help would be greatly appreciated.

You will probably find this thread interesting. tic-tac-toe computer

bascially a bunch of if statements with certain moves of greater priority then others... I did this a couple of months ago but used 0, 1, and 2; then took a nested for loop to dislay all the stuff to the screen... and had another for loop controlling checking for winners and before i had done it this way i just had a bunch of if statements... about 800 lines of code with the for loops it but it down to 100; I may have got of topic with this but I'm saying to basically plan before you program and espicially AI..... ALso check out the article noted about... good luck

Before you move on, you need to fix that indentation. Very important.

The min-max algorithm can be used for this. Research min-max algorithm, and I think once you understand the algorithm, it is easy to program.

yeah min-max would work i thought about telling you that today... and came back to tell you... but another thing i noticed about your code is you variable names... when somebody looks at the code they dont know what m and n do... give them more exact names.. It may be a little longer but it will be easier to understand whats going on