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Follow these steps:
● In a file called sum_recursion, create:
o a function that takes a list of integers and an integer as 2
arguments. The integer will represent an index point.
o This function needs to add the sum of all the numbers in the list
up until and including the given index point by making use of
recursion and no loops.
Examples of input and output:
adding_up_to([1, 4, 5, 3, 12, 16], 4)
=> 25
----------
In my solution, I get 28 instead of 25. When index_num = 5

What I have tried:

```def sum_recursion(index_num, list_numbers):
# When length os a list numbers is equal to 0, the program returns a 0
if len(list_numbers) == 0:
return 0
# When length os index number is greater or equal to length of list numbers, the program returns a 0
elif index_num >= len(list_numbers):
return 0
else:
# Adds sum of all the numbers in the list,up until and including the given index point by making use of recursion
next_index = (index_num + 1, len(list_numbers))[index_num + 1 == 0]
return list_numbers[index_num] + sum_recursion(next_index, list_numbers)
# List and index number declaration
list_numbers = [1,4,5,3,12,16]
index_num = 4
# Prints sum of the list depending on the index
print(sum_recursion(index_num, list_numbers))```
Posted
Updated 26-Jul-22 4:37am
Comments
Richard MacCutchan 26-Jul-22 9:17am
Each time you call the recursive function you should pass the index number minus 1 to the function.
Thandeka Zulu 26-Jul-22 10:45am
def sum_recursion(index_num, list_numbers):
# When length os a list numbers is equal to 0, the program returns a 0
if len(list_numbers) == 0:
return 0
# When length os index number is greater or equal to length of list numbers, the program returns a 0
elif index_num >= len(list_numbers):
return 0
else:
# Adds sum of all the numbers in the list,up until and including the given index point by making use of recursion
next_index = (index_num + 1, len(list_numbers))[index_num + 1 == 0]
return list_numbers[index_num] + sum_recursion(next_index-1, list_numbers)
# List and index number declaration
list_numbers = [1,4,5,3,12,16]
index_num = 4
# Prints sum of the list depending on the index
print(sum_recursion(index_num-1, list_numbers))
-----------------------------------------------
when I add -1.The program gives no result.

## Solution 1

To add to what Richard has said, getting it to run at all does not mean your code is right! :laugh:
Think of the development process as writing an email: compiling successfully means that you wrote the email in the right language - English, rather than German for example - not that the email contained the message you wanted to send.

So now you enter the second stage of development (in reality it's the fourth or fifth, but you'll come to the earlier stages later): Testing and Debugging.

Start by looking at what it does do, and how that differs from what you wanted. This is important, because it give you information as to why it's doing it. For example, if a program is intended to let the user enter a number and it doubles it and prints the answer, then if the input / output was like this:
```Input   Expected output    Actual output
1            2                 1
2            4                 4
3            6                 9
4            8                16```
Then it's fairly obvious that the problem is with the bit which doubles it - it's not adding itself to itself, or multiplying it by 2, it's multiplying it by itself and returning the square of the input.
So with that, you can look at the code and it's obvious that it's somewhere here:
```int Double(int value)
{
return value * value;
}```

Once you have an idea what might be going wrong, start using the debugger to find out why. Put a breakpoint on the first line of the method, and run your app. When it reaches the breakpoint, the debugger will stop, and hand control over to you. You can now run your code line-by-line (called "single stepping") and look at (or even change) variable contents as necessary (heck, you can even change the code and try again if you need to).
Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. Did it do what you expect? If so, move on to the next line.
If not, why not? How does it differ?
Hopefully, that should help you locate which part of that code has a problem, and what the problem is.
This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development. And like all skills, it only improves by use!

Comments
Thandeka Zulu 26-Jul-22 13:32pm
Thank you.
OriginalGriff 27-Jul-22 0:48am
You're welcome!

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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