Summary: In this laboratory, you will experiment with the use and application of some of Scheme's basic input and output procedures.
a. Make sure that you understand what
are supposed to do. You may find
the reading on input and
the reading on output
b. Ensure that you understand the sample code from the reading on input.
c. Start DrScheme.
For each of part of this exercise, you should use something like
(define val (read))
to read in a value.
> (define val (read))
45> val 45
read to obtain a number. That is, call
read as above and enter a number.
read to obtain a string.
read to obtain a character.
read to obtain a list of numbers.
read to obtain a symbol. Verify that the value you obtained is a symbol using the
read to obtain a list that contains a number, a string, and a symbol.
g. What happens when you use
read to obtain a list and
you hit <Enter> in the middle of the list?
Consider the following sequence of Scheme commands:
(display "Please enter a value and I will square it: ") (define val (read)) (define val-squared (* val val)) (display (string-append "The value of " (number->string val) " squared is " (number->string val-squared))) (newline)
a. What do you expect the code to do?
b. Verify your answer via experimentation.
Rewrite the code from the previous exercise to use
let* (or both) rather than
a. Save the above code in a file (e.g.,
b. Open a terminal window.
c. In that terminal window, type
/usr/local/plt/bin/mzscheme -r file.scm
Where file.scm is the name you chose in part a.
d. Reflect on what happened in step c. Did you need to type any Scheme? Could someone else use step c without understanding the underlying Scheme?
e. Create a file called
square that contains the
#!/bin/bash /usr/local/plt/bin/mzscheme -r file.scm
where file.scm is the name you chose in part a.
f. In the terminal window, type
chmod 755 square
g. In the terminal window, type
h. Reflect on what just happened.
a. What happens in your square program if someone enters something other than a number?
b. Update your program so that it prints a friendly error message
display) and then asks again if someone enters
something other than a number.
a. Write a Scheme program that reads in the three coefficients of a quadratic equation (the a, b, and c in ax2 + bx + c) and prints out the roots of the equation. You should model this program on the previous exercises. In case you've forgotten, the roots of the quadratic equation are
(-b +/- sqrt(b2 - 4ac)) / 2a
b. Save the program in a file and execute it from the command line.
c. Reflect on what happened. Did you need to type any Scheme? Could someone else use step b without understanding the underlying Scheme?
Write a program repeatedly asks for a value and computes its square root. You will probably need to
a. Put the stuff (request for value, computation of a value, display of that value) in a procedure.
b. Have that procedure recurse.
c. Decide upon a base case to stop recursion. (I'd suggest that you stop when someone enters something other than a number.)
Write a command-line version of some simple game that uses
random. For example, you might ask someone to
guess whether the next random number will be even or odd and
give them a point if they guess correctly.
I usually create these pages
on the fly, which means that I rarely
proofread them and they may contain bad grammar and incorrect details.
It also means that I tend to update them regularly (see the history for
more details). Feel free to contact me with any suggestions for changes.
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