Please explain the code, as well as make it easy to understand. Thanks.

Marked Problems. The digit sum function computes the sum of the digits of a nonnegative integer represented in decimal (base 10). For example, the digit sum of 1234 is 1 + 2 +3 +4 = 10. In this question you will complete a C implementation of the digit sum function using two separate methods: iteration and recursion. You will be provided with a file containing the functions prototypes shown below. You must provide complete implementations of each function using the concepts discussed in class. Do not use global or static variables. // digit_sum_iterative(n) returns the decimal sum of the digits in n // requires: 0