[sde]

int isdigit() returns a non-zero if true and a zero if false.

either way it returns an integer.

now i'm not sure on this but perhaps test for zero isntead of boolean.

if (isdigit(date[x]) == 0)  
cout << "Please enter a date dd/mm/yyyy: ";  
else  
cout << "Entry Valid\n";  
};

i'm just guessing here based on this documentation: http://www.mkssoftware.com/docs/man3/isdigit.3.asp