Replace
box.c[i].b[i]="t";
with
box.c[i].b[i]='t';
and it should work.
Please note:
The way you are using your loop only one character in each of the
pls
class char arrays is assigned the 't' value.
If you want to assign each character the 't' value you need to use a second loop.
int main()
{
star box;
for(int i=0;i<8;i++)
{
for(int j=0;i<8;j++)
{
box.c[i].b[j]='t';
}
}
}