Loops

Users are annoying and we have to deal with it part two

Use a while (or do-while) loop to write a program which ensures a user enters a valid integer number. Use cin.fail() along with a variable of type int to detect if the program was unable to read an integer, as before. Now enclose this code in a loop which exits only when a valid integer has been read. Otherwise, it should repeatedly prompt the user for input until they enter something valid.

This is a boring but useful exercise, as you’ll likely need to do this often.

Guessing game

Implement a guessing game using a while loop and conditional statements. It should work as follows:

The program generates a number (start with a hard-coded value as this is simpler to code and easier to test – you can add randomness later).
The player enters their guess.
The program informs the user whether their guess is too high, too low, or correct.
If the guess is correct, the player wins.
Otherwise, the player can guess again until they get it right.

Extension tasks

Make the program generate a random number rather than a hard-coded value.
Limit the number of guesses the user is allowed.
Calculate a score based on the number of guesses the player needed to use.

Hashing a string

The hash of a string is an integer value calculated from the elements of the string. Let’s calculate the hash of a string one character at a time. Start by setting the hash to 0. For each character in the string, add the ASCII value of that character to the hash and then set the hash to its value modulo 23.

Using cin, read one character at a time. The program should exit, and print the hash, when . is entered.

Note: a while loop might be best suited to this task.

Fibonacci numbers

The fibonacci sequence 1, 1, 2, 3, 5, 8, 13, ... can be generated one number at a time, as long as you know the values of the previous two numbers. Start off by defining the first two numbers: 1 and 1. The next number is the sum of the previous two, E.g., the first third number is 1 + 1 = 2, thee fourth number is 1 + 2 = 3.

Write a program to compute the n-th fibonacci number, where n is a value entered by the user.

Note: a for loop might be best for this task, but a while loop also works.

Loop conditions and increments

Write a program which uses a for loop, but no conditional statements, to print out the following sequences of numbers.

Count down from 100 to 1 (inclusive).
Print all the even numbers, in ascending order, from 1 to 50 (inclusive).
Print all the powers of 2 which are less than or equal to 65536.

Nested Loops

Integer Square root

Write a program to find the integer square root of a number. I.e., given a number x, find the number y such that y * y = x. Your program shourd find this number if it exists, or, if it doesn’t, report this to the user (without using the built-in functian!).

Primality testing

Now write a program which checks if a number, n is prime. I.e., if the only two numbers which multiply to give n are 1 and n itself.

Extension task

Is your program as efficient as it can possibly be? Can you skip any checks. E.g., if you’ve checked 3 * 4*, then there is no need to check 4 * 3`.

Ascii-art trees

Write a program to draw ascii-art trees, like this:

    #
   ###
  #####
 #######
#########
    |

Adapt your program to draw trees with custom parameters. I.e., the user should be able to enter the height and trunk length – the tree above has a height of 5 and trunk length of 1.

Finally, decorate the tree: add decorations (*), on alternate rows. Each decoration must be horizontally separated from the next by three #’s, and cannot be on the left or right hand edge of the tree. For example, a tree of height 8` would be decorated like this:

       #
      #*#
     #####
    #*###*#
   #########
  #*###*###*#
 #############
#*###*###*###*#
       |