Write a program that takes a positive integer as input and calculates its factorial using a for loop. The factorial of a number is the product of all positive integers up to that number.

Sure, here is a simple program in Python that calculates the factorial of a number using a for loop:

# Get input from user
num = int(input("Enter a positive integer: "))

# Initialize factorial to 1
factorial = 1

# Check if the number is negative, zero or positive
if num < 0:
   print("Sorry, factorial does not exist for negative numbers")
elif num == 0:
   print("The factorial of 0 is 1")
else:
   for i in range(1,num + 1):
       factorial = factorial*i
   print("The factorial of",num,"is",factorial)

This program first takes an integer input from the user. It then checks if the number is negative, zero or positive. If the number is positive, it calculates the factorial by multiplying all the integers from 1 to the input number using a for loop.