How to make C only accept numbers?

How to make C only accept numbers? If I type 432,234,21. Then the program works just fine. However if I type any kind of string it automatically loops goes inside the else statement that says "Sorry too many unsuccessful attempts".

{    counter = ;    pinNumber = ;    (counter<){        ( , );        pinNumber=(, &pinNumber);        (pinNumber == ){            counter=;        }{            ++counter;            (counter<){                ();            }{                ();                ();            }        }    }}