C++ PROGRAM
# include <iosream.h>
void main( )
{
 char x ;
cout <<"enter a character";
cin >> x;
if ( x >=&& x<='90')
{
  x=x+32;
  cout << x ;
}
else if (x=97 && x<=122)
{
   x=x-32;
   cout << x ;
}
else
{
cout <<"invalid";
}
}