C++ :: Delete Invalid Input Until Correct Input Is Entered?

Program is to add two fractions together like so..

This program adds fractions. ‘Y’ continues, any other key exits program
===================================================
Enter numerator 1 ==> 1
Enter denominator 1 ==> 3
Enter numerator 2 ==> 1
Enter denominator 2 ==> 6
1 1 1
--- + --- = ---
3 6 2
-----------------------------------------------------
Continue? Y or N! ==> n

My question is that i need each input to be a number.
if a character is entered i want it to output something like..

This program adds fractions. ‘Y’ continues, any other key exits program
===================================================
Enter numerator 1 ==> 1
Enter denominator 1 ==> a
You need to enter a number here.
Press any key to continue.

and then clear the part where the letter was entered.

This program adds fractions. ‘Y’ continues, any other key exits program
===================================================
Enter numerator 1 ==> 1
Enter denominator 1 ==>