CMSC 106 Project #1 Fall 2001


Due date: 11:00 pm on Monday, September 24, 2001.

Purpose

In this project you are to write a C program which will declare variables, read values into and write the values stored in those variables, and perform various calculations and assignments using them. You will also have the opportunity to become familiar with the system facilities to be used for developing projects in this course: several basic UNIX commands, the text editor, the C compiler, and the ``submit'' program used for electronic project submissions.

Imagine that you are developing a system to help a weather station process weather observations (temperature, wind, air pressure, and humidity). The purpose of the program is to help convert data from one set of units to another, to calculate the wind speed from the motion of a weather balloon, and to express humidity data in different forms. In order to be able to handle data collected in different formats, you must be able to convert from various units of measure to other units. Your program will prompt the user to enter values in certain units and then print out both the original values and the values in the other units.

Project description

You will be required to write a C program to do the conversions explained in this section. As you read this section, you may also want to refer to the ``Sample output'' section below.

Your program is to first print certain introductory information and read certain required input values from the user. It will then print 4 separate sections of output giving the calculated values.

Identification and input

Your program must first print a welcome message: Welcome to ``Weather Wizard'' Unit Converter! ``Weather Wizard'' must be printed in double quotes as shown above. The program must then request a set of temperature and air pressure values in English units (degrees Fahrenheit and inches of mercury). There must be a blank line between any two requests for values. This section should be preceded by the message: Please enter values in `ENGLISH' units: The word ``ENGLISH'' must be printed in single quotes as shown above. Following this message, the program must prompt the user on a separate line to enter a temperature in degrees Fahrenheit. This prompt must contain the exact words ``temperature'' and ``Fahrenheit''. The program must then read in a single temperature value. This number will be an integer. Following a blank line, the program must prompt the user to enter a pressure in inches. This prompt must contain the exact words ``pressure'' and ``inches''. The program must then read in a single pressure value. This number will be a positive value, possibly with a fractional part.

The program must then request a set of temperature and air pressure values in metric units (degrees Celsius and millibars). There must be a blank line between any two requests for values. This section should be preceded by the message: Please enter values in `METRIC' units: The word ``METRIC'' must be printed in single quotes as shown above. Following this message, the program must prompt the user on a separate line to enter a temperature in degrees Celsius. This prompt must contain the exact words ``temperature'' and ``Celsius''. The program must then read in a single temperature value. This number will be an integer. Following a blank line, the program must prompt the user to enter a pressure in millibars. This prompt must contain the exact words ``pressure'' and ``millibars''. The program must then read in a single pressure value. This number will be a positive value, possibly with a fractional part.

Following a blank line, the program must then print a header message for the wind calculator. This message must contain the exact words ``Wind'' and ``Calculator''. On the next line, the program is to print a prompt for the user to enter the number of miles and feet traveled by the weather balloon. The program must then read in a value for the miles and a value for the feet traveled. These numbers will be non-negative integers. On the next line, the program is to print a prompt for the user to enter the amount of time the balloon has been traveling, in minutes and seconds. The program must then read in a value for the minutes and a value for the seconds of time. These numbers will be non-negative integers.

Following a blank line, the program must then print a header message for the humidity calculator. This message must contain the exact words ``Humidity'' and ``Calculator''. On the next line, the program is to print a prompt for the user to enter the Fahrenheit air temperature and dew point temperature. The program must then read in 2 values representing the appropriate temperatures. These numbers will be integers.

Your program may assume, without checking, that the user will enter the proper number of values which will be of the types described above and whose values will always be within the ranges indicated.

First output section-English to metric units

After the input values are read, your program is to print 10 asterisks ($*$) preceded and followed by blank lines, followed by its first section of output. The first line of this output section must contain the phrase ``English to metric conversion''. The next line of output must contain the Fahrenheit temperature value read in, followed by the equivalent temperature in Celsius. Both temperature values must be printed on the same line, and each value must be labeled in the appropriate units. The temperature values should be printed rounded to the nearest whole degree. On the next line, the program must print the air pressure value read in, followed by the equivalent value in millibars. Both pressure values must be printed on the same line, and each value must be labeled in the appropriate units. The value in inches must be printed with an accuracy of 2 decimal places, and the value in millibars must be printed rounded to the nearest whole millibar.

Second output section-metric to English units

After the first output section is printed, your program is to print a blank line followed by its second section of output. The first line of this output section must contain the phrase ``Metric to English conversion''. The output for this section will follow the same pattern as the first section above, except the metric units read in will be followed by their equivalent English units. The values must be printed with the same accuracy and the same labeling as described for the first output section above.

Third output section-wind calculator

After the second output section is printed, your program is to print a blank line followed by its third section of output. The first line of this output section must contain the phrase ``Wind calculator results''. On the next line, the program must print the wind speed in feet per second, miles per hour, and knots. The three values are to be labeled ``feet/sec'', ``mph'', and ``kt'' respectively. The value in feet/sec must be printed with an accuracy of 2 decimal places, and the values for mph and kt are to be printed rounded to the nearest whole unit.

Fourth output section-humidity calculator

After the third output section is printed, your program is to print a blank line followed by its fourth section of output. The first line of this output section must contain the phrase ``Humidity calculator results''. On the next line, the program must print the air temperature, the dew point temperature, and the relative humidity in that order. The temperature values must be printed in units of whole degrees Fahrenheit, and the relative humidity must be printed rounded to the nearest whole percent. The temperatures must be labeled ``degrees F'' and the humidity must be labeled ``%''.

How your program must perform calculations

Here are the conversion factors and formulas the program must use. Note that you MUST use these EXACT conversion factors and formulas, even though you may know of more accurate values. You MUST also use preprocessor macros (symbolic constants) to define any conversion factors or special constants used in the program.

Temperature conversion:


\begin{displaymath}\mbox{TC} = (\mbox{TF} - 32) * 5/9\end{displaymath}


\begin{displaymath}\mbox{TF} = 9/5 * \mbox{TC} + 32\end{displaymath}

where TC is temperature in degrees Celsius and TF is temperature in degrees Fahrenheit

In this project, you should use float variables (or expressions) for quantities which may have a fractional part, and int variables for whole number quantities. Chapters 2-4 of your text don't discuss how expressions which contain both int and float values are evaluated (this is covered in detail in a later chapter). In order to avoid any problems with your calculations, you should realize now that expressions with both int and float values will have a float value when computed.

When writing the expressions for the conversions, be aware that doing the statements in a different order can cause you to get a different answer. For example (52/5200) * 100.0 = 0.0 but (52*100.0)/5200 = 1.0. This is because the 52/5200 is calculated as an integer value since both operands are integer. The answer is actually 0.01, but because it is forced into an integer storage location, only the 0 is stored. Then when it is multiplied by 100.0, the answer is 0.0 because any float times 0 is 0.0. When the second expression is evaluated, the 52 * 100.0 makes it 5200.0 (a floating point number), and then when the division happens, the answer is 1 because there was no truncation of the fractional part. If you have two integers and you want to make sure the result is stored in a float, one easy way is to multiply one of the operands by 1.0 before the other operation is done.

Project requirements

All your C programs in this course should be written in ANSI C, which means they must compile and run correctly with ``cc -std1 -trapuv'' on the OIT UNIX Class Cluster. Even if you already know what they are, you may not use any C language features other than those introduced in Chapters 1 through 4 of your textbook, plus those presented in lecture while these chapters were covered. Note that as a result conditional statements or loops of any type may not be used. Using C features not in these chapters will result in losing credit.

Your program must have a comment near the top which contains your name, login ID, student ID, your section number, your TA's name, and an original description of the action and operation of the program. Do not put your alias in this comment! Your program should be written using good programming style and formatting, as discussed in class and throughout your textbook. For this project, style is considered to consist of:


Developing your program

You may want to skip this section at first, read the rest of the project, and come back to study it carefully when you are about to begin writing your program.

A crucial part of the material to be learned in this course is how to properly develop programs and find the inevitable errors you will make while writing them. This section addresses how to do that. It is not up to the instructional staff to find every error in your program; you need to learn how to find and fix most of them for yourself. If you have tried the techniques below and have still not been able to find or correct a problem, bring a printout of your program (plus printouts of any compiler errors or execution results) to our office hours and we will be able to help you.

Possible development steps

Many people like to write their whole program, or at least have a good outline and idea of what it will look like, before sitting down to type any of it in. That's fine, but it is absolutely essential that you never type in more than a short part of your program without stopping to test what you have so far. You should stop and compile your program, run it on sample input, and verify that it works correctly so far before going on to enter the rest of the program! Of course, as each intermediate stage the part of the program you have entered will obviously not solve the whole problem, and it must at least be a complete and valid C program, but you will find that testing your project at each stage of development will insure you can find and fix any errors more quickly and easily.

For instance, even with a relatively short program like this one you might enter or implement it in steps as follows:


  1. First type in just the part of your program which prints the first two lines, and reads the input values typed in by the user (i.e., the ``Identification and input'' section described above) You will need definitions of symbolic constants for conversion values given and declarations of variables into which the values are to be read. Add debug printf statements to print the values which were read, to make sure these values were read and stored correctly. If not, correct your program before going on!

  2. Next figure out the formulas necessary and add statements to print the first output section). Compile your program and make sure it produces correct results for the part you have entered so far before going on.

  3. Then add the code for the other sections of output.

  4. Lastly, make sure all of the output exactly matches what is specified in the project description. (Placement of words, punctuation, and line breaks should all be double checked.)

In fact, you may want to break each of these steps up into smaller steps- to add statements to print only part of each output section at a time.

Many programs can be developed with equal ease in different orders. The specific steps followed are not important; what is crucial is that you stop and compile and test your program after each one.

Finding compilation errors

  1. Usually the compiler tells you exactly which line in your program is incorrect. If you can't figure out what's wrong by looking at that line, you'll just have to use your textbook or class notes and compare a correct example of that type of statement with what you wrote.

  2. Sometimes the compiler can't always recognize a syntax error immediately (such as when you've forgotten the semicolon which must terminate every C statement), and doesn't notice it until the next line or statement. If the statement the compiler identifies as wrong looks correct to you, try examining the one before it for any errors.

  3. If you see the error ``Invalid statement'' and the compiler identifies the very last line in your program, it usually means you have mismatched braces ({ }). Make sure that there is a closing brace to match the main function's opening brace. Indenting statements between braces in a readable manner will assist in this task.

  4. Here are a couple of unusual compilation errors produced by the cc compiler on the OIT UNIX class cluster and what they mean:

    ld: Unresolved print

    (or scan, or Printf) This means you have misspelled the name of one of the standard library functions (printf as print or Print, scanf as scan, etc.). Every program component must be spelled exactly, and even one incorrect character will cause your program to fail to compile. Check every call to these library functions carefully.

    An unexpected newline character is present in a string literal

    You probably forgot either the opening or closing double-quote mark in one of your printf or scanf argument strings.

    Object file format error... bad file magic number

    The cc C compiler requires that a source file's name end in ``.c''. That's a lowercase ``c'', as in a filename like ``proj1.c''. If your program's filename isn't in that format you must rename it.

Program debugging

It is inevitable that many, if not most or all, of your programs will fail to work correctly as initially written. A few simple strategies can help:

  1. Carefully trace your program through on paper assuming certain input values, and keep track of the current values of all of the variables.

  2. You may need to add debug printf statements to your program to print out the values of variables and calculations. Essentially, this lets the computer trace your program for you. If the printf statements show that your variables or expressions don't contain or produce the values you think they do then that's a clue to what's wrong. Using debug printf statements you can narrow the problem down and determine which variables or expressions don't have the proper values, and then look at those more closely.

  3. If, when you run your program, you get the error ``Floating exception (core dumped)'', this means your program has an unrecoverable execution error. This most likely means you are either trying to calculate some expression containing a division and the denominator's current value is zero, or you are trying to perform some calculation with a float variable which has never been given a initial value and contains a garbage value. To check for the first case, add debug printf statements before every division printing the value of the denominator. To check for the second one, check carefully that all your float variables have initial values or that values are assigned to them or read into them before they are used in calculations.

  4. Another fatal execution error is ``Segmentation fault (core dumped)''. In a program like this one, this message usually is caused by a few mistakes related to the differences between printf and scanf. See your lecture notes where this was discussed, or look at your textbook on pages 39-40.

  5. If your program just hangs and doesn't do anything after you type values to be read into certain variables and you've pressed the enter key, you are likely to be making another error in confusing printf with scanf. See your class notes, or carefully reread pages 39-40.

  6. Note: If you get either of these ``core dumped'' errors. You most likely now have a file named ``core'' in the current directory. Core is the central part of memory, and to dump the core means that it gave you a file containing what core looked like at the time the program died. This is most likely a very large file and most likely something you don't want to read so it is good to delete it to get it out of the way.

  7. If, after you have tried these techniques you still can't figure out why your program doesn't work, bring printouts of your source code and any compiler errors or output produced to our office hours, and we can teach you how to track the problem down.

Further helpful hints

Readable code is important in the real world because most of the programmer's time is spent rewriting or modifying code that already exists - not writing code from scratch. To make your code readable, be sure to use descriptive variable names (English words or their abbreviations), indentiing (so that you can tell what statements are dependant on others), vertical whitespace (blank lines between sections) and comments for the person reading the code. Even though in this class you will not be rewriting someone else's code - anyone of the instructional staff who reads your code will be able to do so much quicker and the grader will be much more likely to be able to follow your code if you make it readable right from the start.

Remember that the vertical spacing (what appears on each line) is up to you as you type. Emacs does not do a word wrap - so if there is a very long line, you should press the enter key to wrap it to the correct position on the next line to make the code as readable as possible.

Keep one or two backup copies of your program saved under different filenames or in different subdirectories of your account. Before making any major changes to your program, copy it to a new backup file with a different name. This will save you a lot of time if you accidentally delete your file, or if it turns out that your changes were incorrect and you want to quickly revert to the previous version without having to undo all of your modifications by hand.

Always start all your projects as soon as they are assigned! If you end up having a problem which you can't solve on your own you will have plenty of time to come to office hours for help. If you wait until right before a project is due and you run across such a problem it's too late to get help without having to submit your project late and lose credit.

Academic integrity statement

Any evidence of unauthorized use of computer accounts or cooperation on projects will be submitted to the Student Honor Council, which could result in an XF for the course, suspension, or expulsion from the University. Projects are to be written INDIVIDUALLY. For academic honesty purposes, projects are to be considered comparable to a take-home exam. Any cooperation or exchange of ideas which would be prohibited on an exam is also prohibited on a project assignment, and WILL BE REPORTED to the Honor Council.


VIOLATIONS OF ACADEMIC HONESTY INCLUDE:


  1. failing to do all or any of the work on a project by yourself, other than assistance from the instructional staff.

  2. using any ideas or any part of another student's project, or copying any other individual's work in any way.

  3. giving any parts or ideas from your project, including test data, to another student.

  4. having programs on an open account or on a PC that other students can access.

  5. transferring any part of a project to or from another student or individual by any means, electronic or otherwise.


IT IS THE RESPONSIBILITY, UNDER THE UNIVERSITY HONOR POLICY, OF ANY STUDENT WHO LEARNS OF AN INCIDENT OF ACADEMIC DISHONESTY TO REPORT IT TO THEIR INSTRUCTOR.

Submitting your project

Your project must be electronically submitted by the date above, before 11:00 pm, to avoid losing credit as indicated on the syllabus. No projects more than two days late will be accepted for credit without prior permission or a valid medical excuse, as described on your syllabus. Only the project which you electronically submit, according to the procedures provided, can be graded; it is your responsibility to test your program and verify that it works properly before submitting. Lost passwords or other system problems do not constitute valid justifications for late projects, so do not put off working on your program or wait to submit it at the last minute!

Turn in your assignment using the ``submit'' program provided by your instructor. You are to submit only the .c file containing your source code, not the executable version of your program!

If your source code was in a file named ``converter.c'', submit would be run to turn it in as shown:


% submit  1  converter.c

In order to execute either submit command above you must have previously run the ``setup'' command in your instructor's posting account, as described in discussion section and mentioned again below. If you do not see a message saying your submission was successful then your project was not turned in. Try again, or come to office hours for assistance.

Before you submit your project, you must exactly follow the specific submission checklist in the ``Testing a project before submitting'' handout separately posted by your instructor!

Sample output

Here is a sample output, assuming the executable version of the program is in a file named ``wizard''. Underlined text is typed in as input when the program is run, while everything else is written as its output. The output would vary if different values were entered for any of the underlined input values. Be sure to test your program against a variety of inputs, so you are sure it works in all circumstances!

% wizard

Welcome to "Weather Wizard" Unit Converter!
Please enter values in `ENGLISH' units:
Enter Fahrenheit temperature: 86

Enter pressure in inches: 29.53

Please enter values in `METRIC' units:
Enter Celsius temperature: 20

Enter pressure in millibars: 1000

Wind Calculator
Enter miles and feet traveled: 1 1000
Enter number of minutes and seconds elapsed: 1 28

Humidity Calculator
Enter Fahrenheit air temperature and dew-point temperature: 86 68

**********

English to metric conversion
Temperature: 86 Fahrenheit 30 Celsius
Pressure: 29.53 inches 1000 millibars

Metric to English conversion
Temperature: 20 Celsius 68 Fahrenheit
Pressure: 1000 millibars 29.53 inches

Wind calculator results
Wind: 71.36 feet/sec 49 mph 42 kt

Humidity calculator results
Temperature 86 degrees F Dew point 68 degrees F Relative humidity 55%

Class announcements- reminder

Be sure to read your instructor's class announcements every time you log in, or frequently on the class webpage, for important information which may be present. You are responsible for the content of these announcements. To be certain to never miss this information, and so you can submit your projects, you must execute the command source ~<instacctID>/setup which will cause these announcements to be displayed whenever you log in (where <instracctID> must be replaced by the name of your instructor's class posting account). This only needs to be done once for the semester, and the announcements will be shown every time you log on afterwards.


Steve Scolnik
2001-09-14

Web Accessibility