Complete the following Python exercises. Test normal inputs, boundary values, and invalid inputs where applicable.

1. Read a learner name and print a personalized welcome message.
2. Read two integers and print their sum, difference, product, and quotient.
3. Convert a temperature from Celsius to Fahrenheit.
4. Read the radius of a circle and print its area and circumference.
5. Format a bill showing item name, quantity, price, and total.