Problem
I. Task I: Write a python program to allow the user to enter their telephone number. Use the input() function to ask users to enter their values. If their entered string consists only of numeric characters and is not blank, print the entered string, else, tell them to enter again, also, tell them that telephone numbers can contain only digits. Hint: use if-else to check whether the entered string consists of only digits or not and a while loop to allow the user to enter again.
II. Task II: Write a python program to allow the user to enter their telephone number. Use the input() function to ask users to enter their input. If their entered input consists only of digits and the length is 10 (i.e, if their entered number has 10 digits), then only print the entered string, else, tell them to enter again, also, tell them that telephone numbers can contain only 10 digits. Hint: use if-else to check whether the entered string consists of only digits or not and a while loop to allow the user to enter again.
III. Task III: Write a python program to ask the user to input a string. Then print the position of each character in the inputted string, in a reversed order, so that the last character appears in the first line. Tips: You can do this with a for-loop statement and the range() function.
IV. Task IV: Build an inventory system. The system should ask the user to input product names till he/she does not have any new product to enter anymore (i.e., an empty product name).