My array is not storing values from the while loop

Question

I am trying to make an array from a loop and I keep getting 0s printed rather then the changes values, there are a few float comments from earlier in the program that are used in the function but I think its a typo as to why it isn't working.

print()
pred_position = zeros(int(600*max_chase_time))
i = 0
j = speedofpredator
while i>0 and 0<max_chase_time:
    pred_position[i] = i + j*0.1
    i = i + 1
print(pred_position)

print()

prey_positions = zeros(int(600*max_chase_time))
b = 0
j = speedofpredator
while b>0 and 0<max_chase_time:
    prey_positions[b] = b + initpositions + j*0.1
    b = b + 1
print(prey_positions)

These are my two loops and arrays.

Please provide a minimal reproducible example, as well as the current and expected output. Have you done any debugging? I would recommend reading ericlippert.com/2014/03/05/how-to-debug-small-programs. — AMC
– AMC, Commented Oct 29, 2020 at 0:03

fuenfundachtzig · Accepted Answer · 2020-10-28 10:11:02Z

2

You initialize i=0 and in your while loop you check i>0. Therefore you don't enter the while loop and skip it. The same thing happens with b in the second loop

edited Oct 28, 2020 at 10:11

fuenfundachtzig

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answered Oct 28, 2020 at 9:36

Tamir

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6 Comments

Megan Rochford Over a year ago

I'm sorry I understand what you are saying but I'm not sure what I should do instead of this. Could you give an example?

Tamir Over a year ago

you wrote i=0 then in your while loop you check i>0 and and 0<max_chase_time. Since 0>0 is False you don't enter the while loop and skip it. if you will run it with i>=0 you will enter the loop (but never exit it since max_chase_time doesn't change and i is always >=0

Megan Rochford Over a year ago

ok so i changed it to 'while b>=0 and 0<max_chase_time:' and got the error IndexError: index 55020 is out of bounds for axis 0 with size 55020, is that because the loop is never ending or because of something else?

Tamir Over a year ago

Like I said you don't exit the loop. therefore your i variable will get bigger each iteration. at some point i>len(pred_position) and you will receive an IndexError

Megan Rochford Over a year ago

Is there a way to stop this? I'm sorry, I'm new to python.

|

Adrian P. · Accepted Answer · 2020-10-28 09:47:16Z

0

Try pred_position.append(i+j*0.1)

answered Oct 28, 2020 at 9:47

Adrian P.

11 bronze badge

1 Comment

Amir Afianian Over a year ago

Please try adding more detail to your responses.

timo · Accepted Answer · 2020-10-28 10:06:39Z

i think you could write it like this

max_chase_time = 600     #secs
speed_of_predator = 30   #meter per seconds
speed_of_prey = 10       #meter per seconds

pred_pos = 0             #pred original position
prey_pos = 5000          #prey original position

current_time = 0         #Current time
prey_is_alive = True     #Current prey status

while current_time < max_chase_time:
    current_time += 1              # increment current_time
    pred_pos += speed_of_predator  # increment pred_pos
    prey_pos += speed_of_prey      # increment prey_distance
    print(current_time, pred_pos, prey_pos)
    
    if (prey_pos - pred_pos) <= 0: # if distance is less or equal 0
        prey_is_alive = False      # the prey is eaten
        break                      # exit loop if prey is dead
    
print("Alive", prey_is_alive)

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