in c program

a) Write a program that allows the user to enter an integer n. The program then outputs the sum of the even digits of the number n. The number n has a maximum of 18 digits (does not have to be checked; decimal number does not have to be checked either.) If a negative number is entered, an error message should appear. Input and output should correspond to the following examples. Enter whole number >=0 (max. 18 digits): 123456789123456789 The sum of the even digits of 123456789123456789 is 40 . Enter whole number >=0 (max. 18 digits): 7 The number must be > on of