Base Case:

If the second number is 0, return the first number. This serves as the stopping condition for the recursion.

Recursive Case:

If the second number is not 0, add 1 to the first number and decrement the second number.

Call the function recursively with the updated values.

• Suppose the user entered 20.
• Initially, addNumbers() is called from main() with 20 passed as an argument.
• The number 20 is added to the result of addNumbers(19) .
• In the next function call from addNumbers() to addNumbers() , 19 is passed which is added to the result of addNumbers(18) .