Understanding Recursion Using Sum of Digits
Explore how to apply recursion to solve the sum of digits problem in C#. Understand breaking down problems into smaller parts, tracing call stack execution, and recognizing base and recursive cases, gaining practical skills in recursive problem solving and C# implementation.
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Previous lessons introduced recursion, explained how the call stack works, and outlined when to use recursion instead of iteration. This lesson applies those concepts in practice. It uses a classic introductory problem, the sum of digits, to reinforce recursive problem-solving techniques.
The problem
Given a number, find the sum of all its digits. For example:
SumOfDigits(123)→1 + 2 + 3 = 6SumOfDigits(456)→4 + 5 + 6 = 15SumOfDigits(9)→9
Simple enough to understand, but how do we solve it recursively?
Thinking recursively
Before writing any code, let’s think about the problem the way a recursive method would.
The key question to ask is: can I solve a smaller version of this problem and use that answer to solve the full problem?
Look at the number 123. ...