[C#]Methods – 13

Write a program that can solve these tasks:
Reverses the digits of a number
Calculates the average of a sequence of integers
Solves a linear equation a * x + b = 0
Create appropriate methods.
Provide a simple text-based menu for the user to choose which task to solve.
Validate the input data:
The decimal number should be non-negative
The sequence should not be empty
a should not be equal to 0

[C#]Next Date

We are given a date (day + month + year). Write a program to print the next day.

[C#]Tribonacci (T n = T n-1 + T n-2 + T n-3) Triangle

You all know the Fibonacci sequence. Well, the Tribonacci sequence is almost the same, but it uses the last three numbers (instead of the last two) to calculate the next number in the sequence. So, we can define each element in the sequence as:
T n = T n-1 + T n-2 + T n-3
where T n is the current Tribonacci number (n is the index of the current Tribonacci number).
The Tribonacci sequence can begin with any three integer numbers – positive or negative – and continue as described by the formula above.
Now, a Tribonacci triangle is a triangle of numbers from the Tribonacci sequence. The first line of the triangle contains only the first number of the Tribonacci sequence. The second line contains the second and third numbers of the Tribonacci sequence, separated by a single whitespace (” “). The third line contains the next three numbers of the Tribonacci sequence (again, separated by whitespaces). The fourth line contains the next four numbers and so on. Basically, every line contains one more number than the previous.
Your task is to write a program, which prints to the console a Tribonacci triangle by given the first three numbers of the Tribonacci sequence, and the number of lines in the triangle.


Asya loves confetti. One day she decided to create exactly N small pieces of sheets with paper size A10.
A10 is a standard for paper sizes. A9 is another standard that is twice as bigger as A10, so A9 can be cut into 2 pieces of size A10. A8 is twice as bigger as A9 and so on. A0 is twice as bigger as A1. See the picture on the left.
Asya has only one sheet of each type (totally 11 sheets). She wants to have exactly N pieces of size A10 by cutting as few sheets as possible.
Asya should not have any wasted sheets.
Write a program for her.
For example if we want to cut sheets into 9 pieces with the size of A10, we will use the only A7 sheet (cut into 8 pieces of size A10) and the only sheet with size A10. Then we will use 2 sheets. All other 9 sheets will not be used.

[C#]Excel Columns

Columns are a fundamental part of any spreadsheet program such as Microsoft Excel. Columns run vertically in a worksheet. Each column is identified by a capital Latin letters in the column header starting with column with identifier A and running through to column with identifier Z. After Z you get AA, AB, AC etc. until you get to AZ. Then it is BA, BB, BC, …, ZY, ZZ, AAA, AAB, …, AAZ, ABA, …, ZZY, ZZZ, AAAA, AAAB and so on… The last column is ZZZZZZZZZZ.

Recently Todor has learned how to work with Excel. Since then all that he do is giving integer indices to every possible column. Starting from the first column A (with index 1), through Z (with index 26), AA (with index 27), and so on. Of course this is a very, very hard and time-wasting job. You, as programmer, know that this can be solved easily with a computer program.
Help Todor by writing a program that converts excel column identifier to a column index.