CODEWITHSUNDEEP
python
Dani
Dani

Reputation: 21

Write 3 positive numbers and sum

I;m writing code, this code should prompts the user for 3 positive numbers (or zero) and then adds them together. If the user enters a negative number, the program should reprompt them until they enter a positive number. But it is not working, when I add negative numbers, the code took it as a part of the final result, and it is supposed that just take the positive. Any help or advice will be more than welcome.

def prompt_number(notPositive):
    print("Invalid entry. The number must be positive.")

def compute_sum(a, b, c):
    return a + b + c

def main():

    while True:
        num1 = int(input("Enter a positive number: "))
        if num1 >= 0:
            print()
        else:
            print(prompt_number(num1))


        num2 = int(input("Enter a positive number: "))
        if num2 >= 0:
            print()
        else:
            print(prompt_number(num2))


        num3 = int(input("Enter a positive number: "))
        if num3 >= 0:
            print()
        else:
            print(prompt_number(num3))
        break
    result = compute_sum(num1, num2, num3)
    print (str(result))

main()

Upvotes: 1

Views: 1724

Answers (2)

AMC
AMC

Reputation: 2702

Review of the code

def prompt_number(notPositive):
    print("Invalid entry. The number must be positive.")

There's probably no need to make a function for this. Not only is the notPositive not following style conventions (it should be not_positive), it isn't even used by the function.

def compute_sum(a, b, c):
    return a + b + c

There's really not much point in having a function just for this, either.

Onto the issue with the main part of the code: when I add negative numbers, the code took it as a part of the final result There's a rather simple reason for that, it's because you never told the program not to. Try walking through the execution of the code on paper.

A possible solution

Clean and straightforward!

def get_pos_num():
    while True:
        curr_val = int(input("Enter a positive integer: "))
        if curr_val >= 0:
            return curr_val
        else:
            input("Invalid input: Not a positive number.\n")


while True:
    print("\nProgram to calculate the sum of 3 positive integers.")
    first_num = get_pos_num()
    second_num = get_pos_num()
    third_num = get_pos_num()
    num_sum = first_num + second_num + third_num
    print(f"You entered the following numbers: {first_num}, {second_num}, {third_num}.")
    print(f"Their sum is: {num_sum}\n")

Let me know if you have any questions :)

Upvotes: 1

Tony Tannous
Tony Tannous

Reputation: 14886

It is because you skip when user input is negative, you should keep looping until the desired input is fed.

def prompt_number(notPositive):
    print("Invalid entry. The number must be positive.")

def compute_sum(a, b, c):
    return a + b + c

def main():
    num1 = -1
    num2 = -1
    num3 = -1
    while num1 < 0:
        num1 = int(input("Enter a positive number: "))
        if num1 >= 0:
            break
        else:
            print(prompt_number(num1))

    while num2 < 0:
        num2 = int(input("Enter a positive number: "))
        if num2 >= 0:
            break
        else:
            print(prompt_number(num2))

    while num3 < 0:
        num3 = int(input("Enter a positive number: "))
        if num3 >= 0:
            break
        else:
            print(prompt_number(num3))

    result = compute_sum(num1, num2, num3)
    print (str(result))

main()

A better solution is to write a get_positive_number method to eliminate code duplication.

def get_positive_number():
    num = -1
    while num < 0:
        num = int(input())
        if num >= 0:
            return num
        else:
            prompt_number()       

def prompt_number():
    print("The number must be positive.")

def compute_sum(a, b, c):
    return a + b + c

def main():
    num1 = get_positive_number()
    num2 = get_positive_number()
    num3 = get_positive_number()

    result = compute_sum(num1, num2, num3)
    print (str(result))

main()

Upvotes: 2

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