Exercicio calculo maior numero python

Question

Good afternoon,

I’m developing an exercise in python, I saw that there are already some similar resolutions in the forum, but I developed one of my own and I’m not understanding the reason for the malfunction (only the value 0 is returned, unless I fall in the if <2, in that case the answer is "ERROR")

It follows code and proposal of the exercise, I thank the help.

Write the maior_prime function that takes an integer number greater than or equal to 2 as parameter and returns the largest prime number less than or equal to the number passed to the function

Note that:

maior_primo(100) deve devolver 97
maior_primo(7) deve devolver 7

def eprimo(k):

  n = 2
  numero = 0

  if k<2:
    return "Teste: Não é possivel calcular"
  else:
    while n<=k:
      if all(n%x!=0 for x in range(2,k)):
        numero=n
        n=n+1
      else:
        n=n+1

  return numero

k=int(input("numero k:"))

print(eprimo(k))

Answer 1

in your check from 1 to 1, you are looking for splitters up to the given maximum number(k), not up to the smallest number you are checking (n):

if all(n%x!=0 for x in range(2,k)):

Exchange for:

if all(n%x!=0 for x in range(2,n)):

and should work.

After tidying up, there is a little space for you to optimize the thing: why start looking for the primes from the lowest number, for example? Would it have any gain if you started from K and were checking the progressively smaller numbers?

Also see if you understand what this line that you need to fix is doing - it’s much more advanced code than the code that you have around - if you don’t understand, it’s nicer to rewrite in a simpler way, than using a magic formula that "more or less works".