Computer Algorithms I CS 305 Class Notes

Lecture Notes for Computer Algorithms I

11 September 2003 - An Interlude on Questions, Answers, and Signedness

Ask Good Questions

Date: Wed, 10 Sep 2003 11:26:12
From: s0------@monmouth.edu
To: rclayton@monmouth.edu
Subject: using send-files

I couldn't get send-files to work.

exit

Where's the important information? Where's the what, when, where, how.
This kind of question just begs for the answer "Gee, that's too bad."

Provide Information

Date: Wed, 10 Sep 2003 11:32:36
From: s0------@monmouth.edu
To: rclayton@monmouth.edu
Subject: I can't get send-files to work

I was trying to send the program from
rockhopper while telnetting in. Does it have
to be sent from an on campus machine?

I followed the instructions on the assignment
page:

  send-files -a 1 -s 305lab1a.cc

It says it can't find "send-files".

Now there's enough information to answer sensibly.

Write Well

Date: Mon, 8 Sep 2003 12:40:24
Subject: assignment 1
From: s0------@monmouth.edu
To: rclayton@monmouth.edu

I was trying to view the get() in the
directory "/export/home/class/cs-305/pa1a"
and it said it wasn't there. Also I had a
question on the assignment with it are we
supposed to have it look, for example
"something.html" or "something"?  that's
assuming that WWW preceds the string.

Ideally, people should look forward to reading your questions.

A Bit about Answers

Some students find my answers "unhelpful."

Date: 10 Sep 2003 10:53:39
From: rclayton@monmouth.edu
To: s0------@monmouth.edu
Subject: Re: Turn in process

  I am having trouble with the turn in
  script, i have tried various
  combinations of -an with parenthesis and
  without, with spaces and without,
  however i continue to get an error.

Stare at the assignment page until you
understand which assignment it is you're
turning in.

There isn't enough information here.
- What were the -a options you used?
- What were the errors?

A Question on Signedness

I have a question about overloaded functions.

#include <iostream>

int f (unsigned int a) { 
  return --a; 
  }

int f (int a) {
  return a++; 
  }

int main() {
  std::cout << f(5);
  }

Why does this program output 6?

Integral Promotion

Just numbers are treated as integers.
You can use casting to indicate type.
```
f(static_cast<unsigned int>(5));
```
Or more simply, use the u suffix.
```
f(5u);
```
Or specify types explicitly
```
const unsigned int i = 5;
f(i);
```

A Puzzle

Unfortunately, integral promotion fails us too.

Both g++ and Forte CC produce errors when compiling f(3000000000);

$ CC -c t.cc
"t.cc", line 7: Error: Overloading ambiguity
between "f(unsigned)" and "f(int)".
1 Error(s) detected.

$

This is non-portable, but not (to me) ambiguous.

A Final Note

What's wrong with

int f(unsigned a) { 
  return --a; 
  }

When a is zero, the value --a is undefined (that is, implementation independent).
This code does not (should not) inspire confidence in the author's abilities.

This page last modified on 11 September 2003.