while loop and range-CodePudding

How to print all numbers in range from two inputs which are divisible by 3 with while loop? If num_1 is smaller than num_2 then step should be increased and how to make it opposite??

num_1 = int(input("First number : "))
num_2 = int(input("Second number : "))
i = num_1
while i in range(num_1, num_2):
    if i % 3 ==0 and num_1 < num_2:
        print(i)
    i  = 1
else:
    if i % 3 ==0 and num_1 > num_2:
        print(i)
i -= 1

CodePudding user response：

You don't need to use a while loop for this. If you want all numbers divisible by three within a given range, you can do this in a single line of code (excluding the inputs):

a = 0
b = 100

l = [x for x in range(a, b) if x%3 == 0]

The result would be:

[0, 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, 42, 45, 48, 51, 54, 57, 60, 63, 66, 69, 72, 75, 78, 81, 84, 87, 90, 93, 96, 99]

You could also make this a function for better reuse:

def get_divisible_numbers(a, b, divisor):
    """
    Returns a list of all numbers between two numbers that are divisible by a given number.
    """
    return [x for x in range(a, b) if x%divisor == 0]

CodePudding user response：

First of all i in range(num_1, num_2) returns type bool, so your while loop will either block or skip.

You can use for instead of while, it will traverse the range(num_1, num_2)

The range function can pass in the step parameter to control the step size, negative numbers are reverse

Use while:

num_1 = int(input("First number : "))
num_2 = int(input("Second number : "))
total = abs(num_1 - num_2)
if num_1 < num_2:
    step = 1
else:
    step = -1
r = range(num_1, num_2, step)

i = 0
while abs(i) < total:
    if r[i] % 3 == 0:
        print(f"i: {i}, v: {r[i]}")
    i  = step

else:
    print('')

Demo:

First number : 1
Second number : 11
i: 2, v: 3
i: 5, v: 6
i: 8, v: 9


First number : 11
Second number : 1
i: -2, v: 3
i: -5, v: 6
i: -8, v: 9

Use for:

num_1 = int(input("First number : "))
num_2 = int(input("Second number : "))
if num_1 < num_2:
    step = 1
else:
    step = -1
for i in range(num_1, num_2, step):
    if i % 3 == 0:
        print(i)

print('')

Demo:

First number : 1
Second number : 11
3
6
9


First number : 11
Second number : 1
9
6
3

CodePudding user response：

There's a number of syntax issues (e.g. indentation). Fixing them up, the following should work:

num_1 = int(input("First number : "))
num_2 = int(input("Second number : "))
i = num_1
while i in range(num_1, num2):
    if i % 3 ==0:
        print(i)
    i  = 1

To handle changing the order of iteration depending on the values of num_1 and num_2 (as asked in a comment), you can do the following:

num_1 = int(input("First number : "))
num_2 = int(input("Second number : "))

if num_1 < num_2:
    for i in range(num_1, num_2):
        if i % 3 == 0:
            print(i)
else:
    for i in range(num_1, num_2 - 1, -1):
        if i % 3 == 0:
            print(i)