#include <cctype>
using namespace std;
 
char input;
 
cout << "Type in a number";
cin >> input;
 
if(!isdigit(input))
{
    // process the number
}

/**********************************************************************
 
 Example #4 -- Boolean expressions
 
**********************************************************************/
 
 
 
#include <iostream>
 
#include <cctype>
 
using namespace std;
 
 
 
int main()
 
{
 
  const bool A = true, B = false;
 
 
 
  const int C = 3, D = 8;
 
 
 
  const char E = 'z', F = '5';
 
 
 
  cout << endl;
 
  cout << "bool A: " << A << endl;
 
  cout << "bool B: " << B << endl << endl;
 
 
 
  cout << boolalpha;
 
  cout << "bool A: " << A << endl;
 
  cout << "bool B: " << B << endl << endl;
 
 
 
  cout << "int C: " << C << endl;
 
  cout << "int D: " << D << endl << endl;
 
 
 
  cout << "C == D: " << (C == D) << endl;
 
  cout << "C != D: " << (C != D) << endl;
 
  cout << "C < 3:  " << (C <  3) << endl;
 
  cout << "C <= 3: " << (C <= 3) << endl;
 
  cout << "C > 3:  " << (C >  3) << endl;
 
  cout << "C >= 3: " << (C >= 3) << endl << endl;
 
 
 
  cout << "C >= 5 || D <= 9: " << (C >= 5 || D <= 9) << endl;
 
  cout << "C >= 0 && D >= 4: " << (C >= 0 && D >= 4) << endl << endl;
 
 
 
  cout << "C != D || C < -6: " << (C != D || C < -6) << endl;
 
  cout << "C <= 0 && D > -6: " << (C <= 0 && D > -6) << endl << endl;
 
 
 
  cout << "1 <= C && C <= 5: " << (1 <= C && C <= 5) << endl;
 
  cout << "1 <= D && D <= 5: " << (1 <= D && D <= 5) << endl << endl;
 
 
 
  cout << "char E: " << E << endl;
 
  cout << "char F: " << F << endl << endl;
 
 
 
  cout << "isalnum( E ): " << isalnum( E ) << endl;
 
  cout << "isalpha( E ): " << isalpha( E ) << endl;
 
  cout << "islower( E ): " << islower( E ) << endl;
 
  cout << "isdigit( E ): " << isdigit( E ) << endl;
 
  cout << "toupper( E ): " << static_cast<char>( toupper( E ) )
 
    << endl << endl;
 
 
 
  cout << "isalnum( F ): " << isalnum( F ) << endl;
 
  cout << "isalpha( F ): " << isalpha( F ) << endl;
 
  cout << "islower( F ): " << islower( F ) << endl;
 
  cout << "isdigit( F ): " << isdigit( F ) << endl << endl;
 
 
 
  return 0;
 
}