Python recursion code help

@will'o'wisp2


So I don't know python but I can help you with the general form of a simple recursive algorithm:

Let's say multby3(n) outputs 3 x n.

So multby3(0) = 0 <- this is known as the base case.

multby3(1) = 3 = multby3(0) + 3
multby3(2) = 6 = multby3(1) + 3
multby3(3) = 9 = multby3(2) + 3
...

So what you have is

multby3(0) = 0
multby3(n) = multby3(n-1) + 3 , (n > 0)

So as pseudo-code this would be




multby3(n) {

// base case
if n = 0 {
output 0 and exit
}

// n > 0
output multby3(n-1) + 3

}





If your first function needs to be able to multiply any two numbers then you'll have to think about how to make a mult(a,b) function but you can follow a similar method.

If you don't understand any of this please let me know.

@will'o'wisp2 I've just edited my post in case you saw it while there were mistakes in it.

i understand what to do now but when i put the code into python, it doesnt do what i want it to do ._.

Can you post your code here and we can take a look?

someone did this for me but i don't really get most of it, isn't there another way to do 5x4 for example?

like i need to do axb basically where a and b can be any number i choose but i'm not really sure how to change that so it works like that

https://cdn.discordapp.com/attachments/322819040059850757/376735193358270467/unknown.png

Which lines do you specifically not understand?

A good way to try and see what the program is doing, is to run it on pen and paper to see what it does to a certain input.

Can you post your code here and we can take a look?

lines 1,3,4,5,7,8,10,11
but anyway
i made some new code but i can't get this one right, i just need to do axb where a and b are any numbers of my choosing, so i've decided to do 3x9 where a is 9 and b is 3

so far i got this

https://cdn.discordapp.com/attachments/322819040059850757/376739815460175874/unknown.png

lines 1,3,4,5,7,8,10,11
but anyway
i made some new code but i can't get this one right, i just need to do axb where a and b are any numbers of my choosing, so i've decided to do 3x9 where a is 9 and b is 3

so far i got this

https://cdn.discordapp.com/attachments/322819040059850757/376739815460175874/unknown.png

Your code doesn't make much sense to me (although I don't know Python). Why do you need two separate functions? And muliple(a) returns an expression containing n but n is not defined in the multiple function? I'm not sure what you're trying to do here.

You could try using this example instead : here is some simple Python code that I just wrote which multiplies a positive integer by 3. Try to understand what it does and then adapt it.







def timesby3(b):
if b == 0:
return 0

return 3 + timesby3(b-1)

print timesby3(12)








https://cdn.discordapp.com/attachments/322819040059850757/376743716263559179/unknown.png

cus then it does this

i justneed to put this in general terms so instead of 3 in need to say a but i dont' know how to do it tho

You're saying "if a = 1" but what is a? The only parameter of the multiply function is n.

@Blue_Cow do you know Python? If you do then it may be better if you help rather than me.

https://cdn.discordapp.com/attachments/322819040059850757/376743716263559179/unknown.png

cus then it does this

i justneed to put this in general terms so instead of 3 in need to say a but i dont' know how to do it tho

x

Do you have a function that works with 3? If not you need to start with that. Or are you adapting my code (I don't think you are).

Why is he using Classes rather than just functions?

Why not use something like this:

def multiply(a, b):
>>>>x = 0
>>>>while b>0: # Assuming b is an integer
>>>>>>>>x += a
>>>>>>>>b -= 1
>>>>return x

Why is he using Classes rather than just functions?

Why not use something like this:

def multiply(a, b):
>>>>x = 0
>>>>while b>0: # Assuming b is an integer
>>>>>>>>x += a
>>>>>>>>b -= 1
>>>>return x

i don't understand what += means? same for -=

nope i can't get it to work either
https://cdn.discordapp.com/attachments/322819040059850757/376746991256076311/unknown.png