Turing/Control Structures and Logical Expressions

For all of these codes, don't forget to put end if/loop/for at the end of the if/loop/for statement.

If statements

Now, try this code:

   var text : string
   get text
   if (text = "Hello") then
       put "Hello, world"
   elsif (text = "Bananas") then 
       put "Bananas are good"
   else 
       put "Bye."
   end if 

• If the user enters "Hello, world" then the output is "Hello"
• If the input is "Bananas" then the output is "Bananas are good"
• If the input is anything else, then the ouput is "Bye."

Loops

Loops do exactly what they sound like. The program from the loop to the end loop Try this code:

   var a : int := 0
   loop
   put a
   a := a + 1
   end loop

This program should output numbers indefinitely from 0 up. Now, let's say that we want to only put the numbers from 0 to 100. We need to put an 'exit when' statement.

   var a : int := 0
   loop
   put a
   exit when a = 100 %put the exit when right here
   a := a + 1
   end loop

For statements

For statements are really useful. The program:

   for i : small..big by intervals
   end for

is the same as

   var i : real := small
   loop
   exit when i = big
   i := i + intervals
   end loop

If that was confusing, a for statement pretty much gives the variable 'i' all the values from small to big.

  for i : 1..10
  put i, ", "
  end for

would output

  1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 

They are really useful for assigning values to an entire array, for example, this program gives the value '0' for every value in the array.

  var asdf : array 1..10,1..10 of int   
  for i : 1..10
  for j : 1..10
  asdf (i,j) := 0
  end for 
  end for

Exercises

1. Make the user input a user name and password. (Hint: If statement)
2. Make the program give the user as many tries as they want, or if you want a challenge, 5 tries (Hint: Loop)
3. Re-do exercise 2 (input 10 values from an array) from the last one, with for statements

Project: Turing

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