计算圆形物体的每平方成本

Question

I am trying to calculate the cost per square of a circular object, given its diameter and price.

Here is what I got:

import math

def main():
    print("This program calculates the cost per square inch of a circular object.")

    diameter = eval(input("What is the diameter of the object? "))
    price = eval(input("What is the price of the whole object? "))

    cost_per_square = (math.pi * (diameter / 2)**2) / price

    print("The cost per square inch is $", round(cost_per_square, 2), sep="")

main()

I'm not good at math, so I wondered if the formula is correct ?

Answer 1

Yes, the formula for the area of a circle is A = π * r * r.

But price should be in the numerator and area in the denominator. You've coded the inverse - square feet per unit cost. Think of the units you want: cost per square foot. That will guide you.

I'd recommend dividing diameter by 2.0 rather than 2 to avoid issues with integer division.

Answer 2

I would also suggest to compute intermediate values with proper names first. This often prevents mistakes in the first place:

radius = diameter / 2.0
area = math.pi * radius**2
price_per_area = price / area

You also might have noticed that I preferred "price" before "cost" and "area" before "square". That's because using synonyms interchangeably also introduces room for errors. All three lines now are so simple that it will be hard to introduce the error you first made.

Answer 3

The formula to find area of circle is pi*r*r . To get the cost per square inch, do this: price / area