1. Display a message for asking your first name, and then use your first name display a greeting message, e.g. Hello, John!.

2. Write a program to calculate the sum from 20 to1. Use for loop to do the calculation.

3. Write a complete C++ program that asks the user to enter the necessary information about the cube, calculate the volume in a function (named as calculate_vol, using reference to pass the volume value out), then display the cube volume in main function. The volume of cube is:

Vol_Cube = d³

Where d is the length.

4. Declare a vector container. Using keyboard to input several floating point numbers, say at least five floating point numbers; find the biggest number and display the result.