Code loops when character entered in C - c

Question

This is mostly out of curiosity to why this is happening as it doesn't matter in my case. If I type in an invalid number it properly goes to the repeat label and asks me to enter a number again, but if i enter in a character like 'f' it will loop endlessly and not stop. Why is this?
The array and all variables here are of type int.
repeat:
printf("Enter number of available space, you are %c: ", userXO);
scanf("%d", user);
switch (*user)
{
case 1: if (spaces[0][0] == 49){ spaces[0][0] = userXO;}else goto repeat; break;
case 2: if (spaces[0][1] == 50){ spaces[0][1] = userXO;}else goto repeat; break;
case 3: if (spaces[0][2] == 51){ spaces[0][2] = userXO;}else goto repeat; break;
case 4: if (spaces[1][0] == 52){ spaces[1][0] = userXO;}else goto repeat; break;
case 5: if (spaces[1][1] == 53){ spaces[1][1] = userXO;}else goto repeat; break;
case 6: if (spaces[1][2] == 54){ spaces[1][2] = userXO;}else goto repeat; break;
case 7: if (spaces[2][0] == 55){ spaces[2][0] = userXO;}else goto repeat; break;
case 8: if (spaces[2][1] == 56){ spaces[2][1] = userXO;}else goto repeat; break;
case 9: if (spaces[2][2] == 57){ spaces[2][2] = userXO;}else goto repeat; break;
default: goto repeat; break;
}

Answer 1

scanf("%d", user); tries to read a number, finds a char(f), leaves it in the buffer and ends. The loop then loops around and executes scanf("%d", user); again. And again...

Answer 2

Here is how I would have written what you did:
int rc, user;
char buf[100];
for (;;) // repeat until explicitly broken out of
{
printf ("Enter number of available space; you are %c: ", userXO);
if (!fgets (buf, sizeof buf, stdin)) /* end of file or i/o error? */
break;
rc = sscanf(buf, "%d", &user);
if (rc != 1) /* other than one parsed input item is an error */
{
printf ("invalid number; try again\n");
continue;
}
/*
* this switch has the odd property of potentially
* doing all 9 cases for case 1, 8 cases for case 2, etc.
* Maybe explicit breaks for success are needed?
*/
switch (user)
{
case 1: if (spaces[0][0] == 49) spaces[0][0] = userX0; else continue;
case 2: if (spaces[0][1] == 50) spaces[0][1] = userX0; else continue;
case 3: if (spaces[0][2] == 51) spaces[0][2] = userX0; else continue;
case 4: if (spaces[1][0] == 52) spaces[1][0] = userX0; else continue;
case 5: if (spaces[1][1] == 53) spaces[1][1] = userX0; else continue;
case 6: if (spaces[1][2] == 54) spaces[1][2] = userX0; else continue;
case 7: if (spaces[2][0] == 55) spaces[2][0] = userX0; else continue;
case 8: if (spaces[2][1] == 56) spaces[2][1] = userX0; else continue;
case 9: if (spaces[2][2] == 57) spaces[2][2] = userX0; else continue;
default: continue;
}
break; /* if valid case(s) taken, exits loop */
}
As you can see, there is no need for a label or a goto. Also the code is more compact.