C++ - my for loop is not starting - c++

Question

I wrote this code for java first. It should print the 2D array as a spiral. I wanted to try it in c++.. in java; there was a draw method. But c++ is not accepting array as a return type (can done by pointers) so I deleted the draw method and copied inside the main method. I commented the draw method where starts and ends. But now; the for loop which is after the draw method (i commented it too) is not starting. What's the problem; I cannot see it... Thanx for help.
int T ;
scanf("%d", &T);
int num[T];
for(int i = 0; i < T; i++){
scanf("%d", &num[i]);
}
for(int m = 0; m < T; m++){
int n = num[m];
int a[n][n];
//draw -start
int all = n*n;
int x = 0, y=0;
for(int counter=1; counter<=all; counter++){
for(int i = 0; i < n; i++){
a[x][y] = counter++;
y++;}
x++; y--;
for(int i = 0; i < n-1; i++){
a[x][y] = counter++;
x++;}
x--; y--;
for(int i = 0; i < n-1; i++){
a[x][y] = counter++;}
x--; y++;
for(int i = 0; i < n-2; i++){
a[x][y] = counter++;}
y++; x++; n = n-2;}
//draw - end
//this for is not starting
for(int i = 0; i<n; i++){
printf("a");
for(int j = 0; i<n; j++){
printf("a");
printf("%d ", a[i][j]);
}
printf("\n");
}

Answer 1

You decrement n in the biggest cycle.
n = n-2;
This is why n < 0 when you reach the for you speak of and it is not looping.
I am almost certain you did not meant to modify n in this loop.

Answer 2

I neatened up your code and provided my answer in the comments.
int T ;
scanf("%d", &T);
int num[T];
for(int i = 0; i < T; i++){
scanf("%d", &num[i]);
}
for(int m = 0; m < T; m++){
int n = num[m];
int a[n][n];
//draw -start
int all = n*n;
int x = 0, y=0;
for(counter=1; counter<=all; counter++){
for(int i = 0; i < n; i++) {
a[x][y] = counter++;
y++;
}
x++;
y--;
for(int i = 0; i < n-1; i++) {
a[x][y] = counter++;
x++;
}
x--;
y--;
for(int i = 0; i < n-1; i++) {
a[x][y] = counter++;
}
x--;
y++;
for(int i = 0; i < n-2; i++) {
a[x][y] = counter++;
}
y++;
x++;
n = n-2; //n = n - 2; all = n * n times?
}
for(int i = 0; i<n; i++){
printf("a");
for(int j = 0; i<n; j++){
printf("a");
printf("%d ", a[i][j]);
}
printf("\n");
}
}
in particular look at this line
n = n-2; //n = n - 2; all = n * n times?