Re-assign value to variable if rand() repeats a number - c

Question

I am making a tic tac toe game in which the user competes against the computer. Whenever the person chooses a spot between 1 and 9, the computer needs to choose one too. For this, I am using rand(). However, if the spot is already taken, I need the computer to calculate a new one. I've tried using while and do-while loops but when I apply them, cmd stops working and doesn't let me continue the game.
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
typedef struct symbol{
int marcado;
char simbolo;
} SPOT;
SPOT casilla1 = {0,'1'};
SPOT casilla2 = {0,'2'};
SPOT casilla3 = {0,'3'};
void table();
void User();
void AI();
int main(){
system("cls");
User();
AI();
Check();
return 0;
}
void table(){
printf("\n %c | %c | %c ",spot1.symbol,spot2.symbol,spot3.symbol);
}
this is the function in which the user chooses a spot:
void User(){
char choice;
do{
do{
board();
printf("\n\nChoose a spot: ");
fflush(stdin);
scanf("%c",&choice);
}while(choice < '1' || choice > '3');
switch(choice){
case '1': if(choice == '1'){
system("cls");
if(casilla1.marcado == 1){
printf("\noccupied\n");
}
else if(casilla1.marcado == 0){
casilla1.marcado = 1;
casilla1.simbolo = 'X';
AI();
}
}
break;
case '2': if(choice == '2'){
system("cls");
if(casilla2.marcado == 1){
printf("\noccupied\n");
}
else if(casilla2.marcado == 0){
casilla2.marcado = 1;
casilla2.simbolo = 'X';
AI();
}
}
break;
case '3': if(choice == '3'){
system("cls");
if(casilla3.marcado == 1){
printf("\noccupied");
}
else if(casilla3.marcado == 0){
casilla3.marcado = 1;
casilla3.simbolo = 'X';
AI();
}
}
break;
}while(Check() != 0 && Check() != 1);
}
and this is the function for the computer. In which I am having trouble in the 'else if' statements since I don't know what to put in them.
void AI(){
int random;
srand(time(NULL));
random = rand() % 3 + 1;
if (random == 1){
if(casilla1.marcado == 0){
casilla1.simbolo = 'O';
casilla1.marcado = 1;
}
else if(casilla1.marcado == 1){
random = rand() % 3 + 1
}
}
if (random == 2){
if(casilla2.marcado == 0){
casilla2.simbolo = 'O';
casilla2.marcado = 1;
}
else if(casilla2.marcado == 1){
random = rand() % 3 + 1;
}
}
if (random == 3){
if(casilla3.marcado == 0){
casilla3.simbolo = 'O';
casilla3.marcado = 1;
}
else if(casilla3.marcado == 1){
random = rand() % 3 + 1;
}
}
}
As I said before, I've tried putting the whole AI() inside the different types of loops, putting only rand() inside them, and so on, and still can't get it to work.

Answer 1

First, choose your data structures better. Instead of:
SPOT casilla1 = {0,'1'};
SPOT casilla2 = {0,'2'};
SPOT casilla3 = {0,'3'};
use
SPOT casilla[3] = { {0,'1'}, {0,'2'}, {0,'3'} };
As a consequence, the switch constructs are not needed any longer. Instead of:
if(casilla1.marcado == 0){
if(casilla2.marcado == 0){
if(casilla3.marcado == 0){
use:
if(casilla[random-1].marcado == 0){
the person chooses a spot between 1 and 9
and
random = rand() % 9 + 1;
You only have 3 casilla. Where are the other 6?
I've tried using while and do-while loops
In AI() there are no loops. Maybe you can show us a code with loops?
printf("\n\nChoose a spot: ");
fflush(stdin);
You probably wanted to fflush() stdout?