Question

The formula for calculating the amount of money in a savings account that begins with an initial principal value (P) and earns annual interest (i) for (n) years is: P(1 + i)ⁿ
Note that i is a decimal, not a percent interest rate: .1 NOT 10%

             Write a python program that does the following:

• Prompt the user on three lines for principal, percent interest rate and number of years to invest (using descriptive prompts)
  • Use a while loop to keep prompting until entries are valid
• Call your function calc_compound_interest() that:
  • takes the arguments principle, int_rate, years
  • uses the above formula to calculate the ending value of the account
  • returns the value
• Call a second function calc_compound_interest_recursive() that:
  • takes the arguments principle, int_rate, years
  • calculates the value recursively – calling a base calculation over and over instead of using the number of year as an exponent.
  • return that value
• Print both values with clear descriptions and formatted with thousand commas and 2 decimal places. Then print whether the two values are equal when rounded to 4 decimal places.

Answer 1

Code:

import math


def calc_compound_interest():
    ''' Asks user to input principle, interest and years to invest
        and calculates the end value using power function of math library.
    '''
    principle = float()  # initialize principle
    int_rate = float()  # initialize int_rate
    years = int()  # initialize years
    while type(principle) != 'float' or type(int_rate) != 'float' or type(
            years) != 'int':  # Check if the user inputs are of the right type
        try:
            principle = float(input('Enter the principle amount: '))  # Prompts user for principle
            int_rate = float(input('Enter the rate of interest: '))  # Prompts user for rate of interest
            years = int(input('Enter the number of years to invest: '))  # Prompts user for years
            break;
        except:
            continue

    end_val = principle * pow((1 + int_rate), years)  # Calculate the end value

    return end_val


def calc_compound_interest_recursive():
    principle = float()  # initialize principle
    int_rate = float()  # initialize int_rate
    years = int()  # initialize years
    while type(principle) != 'float' or type(int_rate) != 'float' or type(
            years) != 'int':  # Check if the user inputs are of the right type
        try:
            principle = float(input('Enter the principle amount: '))  # Prompts user for principle
            int_rate = float(input('Enter the rate of interest: '))  # Prompts user for rate of interest
            years = int(input('Enter the number of years to invest: '))  # Prompts user for years
            break;
        except:
            continue

    # Calculates the end value
    for y in range(years):
        if y == 0:
            end_val = principle * (1 + int_rate)
        else:
            end_val = end_val * (1 + int_rate)

    return end_val


def main():
    pow_val = round(calc_compound_interest(), 2)  # Round upto 2 decimals
    base_val = round(calc_compound_interest_recursive(), 2)  # Round upto 2 decimals
    print(f'End Value using power function= {"{:,}".format(pow_val)}')  # Print using commas
    print(f'End Value without using power function= {"{:,}".format(base_val)}')  # Print using commas


main()

Output:

Keep asking for inputs until vaild input is entered: