Exercises

Please complete each exercise or answer the question before reviewing the posted solution comments.

Use the clear command before starting your work on a new problem to ensure that any existing variable name assignments don't interfere with your work on the new problem.

1. Write a program that asks the user for the distance (in miles) to school and whether it is raining or not and then displays a message according to the table below.

   distance	raining	message
   less than or equal to 1 mile	no	walk
   	yes	walk
   more than 1 mile and less than 10 miles	no	bike
   	yes	bus
   more than 10 miles	no	bus
   	yes	bus

   Here's one program that will work. There are many others that will work also.

   % Transportation.m 
   % Author: Deb Deppeler, Oct 30, 2006
   
   % Get the user input
   distance = input('How many miles from school do you live? ');
   raining  = input('Is is raining (1-yes and 0-no) ? ');
   
   % Determine the mode of transportation to get to school
   if distance > 10
       disp('take the bus');
   elseif distance > 1
       if raining == 1
           disp('take the bus');
       else
           disp('ride your bike');
       end
   else
       disp('walk to school');
   end
   

   How would you change this program so that it didn't ask the user if it was raining unless they answered that the distance was greater than 1 mile and less than 10 miles?

2. Write a program that allows the user to play the game rock, paper, scissors against the computer.

   Here's some pseudo-code to help you get started:

   1. Assign the values 1 to ROCK, 2 to PAPER and 3 to SCISSORS.
   2. Randomly generate a value between 1 and 3.
   3. Ask the user for ROCK, PAPER, or SCISSORS. Hint: have them answer as an integer 1-rock, 2-paper, and 3-scissors.
   4. Check that their answer was between 1 and 3 inclusive.
      • If it was not, display an appropriate error message and exit the program.
   5. Determine winner as indicated by this table.
   6. Display a message that includes what the computer's choice was and wheter the user won or not.

   Computer's Choice	User's Choice	Output Message to Display
   ROCK	ROCK	It's a tie
   ROCK	PAPER	You win, PAPER lays on top of ROCK
   ROCK	SCISSORS	I win, ROCK breaks SCISSORS
   PAPER	ROCK	I win, PAPERlays on top of ROCK
   PAPER	PAPER	It's a tie
   PAPER	SCISSORS	You win, SCISSORS cuts PAPER
   SCISSORS	ROCK	You win, ROCK breaks SCISSORS
   SCISSORS	PAPER	I win, SCISSORS cuts PAPER
   SCISSORS	SCISSORS	It's a tie

   Here's one program that will work. There are many others that will work also.

   % RPS.m
   % Author: Deb Deppeler, Oct 30, 2006
   clear; clc;
   
   % Assign constant values to make program easier to read
   ROCK = 1;
   PAPER = 2;
   SCISSORS = 3; 
   
   % Display intro message to user
   disp( 'Let''s play ROCK-PAPER-SCISSORS ');
   disp( 'Each of us picks ROCK, PAPER, or SCISSORS and I''ll determine who wins.');
   
   % Randomly choose for the computer
   r = randperm(3); % randomly generate values from 1-3
   c = r(1);        % pick the first one for the computer
   disp( 'I have picked my object, now it''s your turn ');
   
   % Get the user's choice
   u = input('Choose 1-ROCK, 2-PAPER, or 3-SCISSORS: ');
   
   % Check for valid choice
   if u < 1 | u > 3
   
       disp('ERROR: Your choice was not 1,2 or 3. You lose.');
   
   else   % If it was valid choice, determine the output message
   
       if c == u
           disp( 'It''s a tie!' );
       elseif c == ROCK & u == PAPER
           disp( 'You win. PAPER lays on top of ROCK.' );
       elseif c == ROCK & u == SCISSORS
           disp( 'I win. ROCK breaks SCISSORS.' );
       elseif c == PAPER & u == ROCK
           disp( 'I win. PAPER lays on top of ROCK.' );
       elseif c == PAPER & u == SCISSORS
           disp( 'You win. SCISSORS cuts PAPER.' );
       elseif c == SCISSORS & u == ROCK
           disp( 'You win. ROCK breaks SCISSORS.' );
       elseif c == SCISSORS & u == PAPER
           disp( 'I win. SCISSORS cuts PAPER.' );
       else
           disp( 'I''m confused.  I didn''t think this could happen.  CHECK CODE' );
       end
   
   end
   

   Note the use of two single quote characters ('') in an output string. Do this when you want to output a single quote character (') as part of a string of characters.

3. Write a code fragment that displays whether or not the value in a variable named x is a prime number or not. If is not a prime number, also display whether it is even or not.

   Hint: A code fragment is not a complete program, it assumes that other code has been executed first. In this case, it assumes that the variable x has already been assigned a value.

   if prime(x)
      disp( [num2str(x) , ' is a prime number' ] );
   else
      disp( [num2str(x) , ' not a prime number' ] );
      if rem(x,2) == 0
          disp( [num2str(x) , ' is an even number' ] );
      end
   end
   

   The rem() function returns the remainder of dividing the first argument by the second. In this case, it returns the integer remainder of dividing the value in x by 2. This works because if rem(x,2) equals 0 than we know that x is even.