Problem Statement

Write a program to print the sum of the first n prime numbers, where n is provided as input from the user.

Handling Input

def main():


main()

Handling Input

def positive_input():
    x = int(input("Enter a positive integer: "))
    while x <= 0:
        print("Invalid input!")
        x = int(input("Enter a positive integer: "))
    return x


def main():
    n = positive_input()


main()

Prime Numbers

def is_prime(n):

Prime Numbers

def is_prime(n):
    for i in range(2, n):

Prime Numbers

def is_prime(n):
    for i in range(2, n):
        if n % i == 0:
            # i equally divides n

Prime Numbers

def is_prime(n):
    for i in range(2, n):
        if n % i == 0:
            return False
    # what if we don't return false?

Prime Numbers

def is_prime(n):
    for i in range(2, n):
        if n % i == 0:
            return False
    return True

Main Function

def main():
    n = positive_input()
    count = 0
    i = 2
    sum = 0
    while count < n:
        if is_prime(i):
            sum = sum + i
            count = count + 1
        i = i + 1
    print("The sum of the first {} prime numbers is {}".
           format(n, sum))

Full Program

def positive_input():
    x = int(input("Enter a positive integer: "))
    while x <= 0:
        print("Invalid input!")
        x = int(input("Enter a positive integer: "))
    return x


def is_prime(n):
    for i in range(2, n):
        if n % i == 0:
            return False
    return True


def main():
    n = positive_input()
    count = 0
    i = 2
    sum = 0
    while count < n:
        if is_prime(i):
            sum = sum + i
            count = count + 1
        i = i + 1
    print("The sum of the first {} prime numbers is {}".format(n, sum))


main()

Testing

• Main Function
• Prime Function

2 + 3 + 5 + 7 + 11 + 13 + 17 + 19 + 23 = 100