Tanda X Angka C++

#include <iostream.h>

main()
{
int a, b, c;
cout<<"input = ";
cin>>a;
for (b=1;b<=a;b++)
{
for (c=1;c<=a;c++)
{
if (c==b||c==a-(b-1))
cout<<c;
else
cout<<" ";}
cout<<endl;
}}