Note

You can do this lab using the graphic environment (Konqueror+Kwrite) or in a terminal using vi as you wish. You can write a Makefile if you feel it will save you time in the lab.

Set up

Login. Change directory to cs201. Make a new directory lab04 and change directory to it. Perform all the exercises in this lab under this directory.

Fixing ifs, whiles and conditions

Download this program [ largest.cpp ] , compile it: The following should find a mistake I planted in the code:

 		g++ -o largest largest.cpp

Try to figure out what I have deleted from it.

Fix it, compile, and test it by running this command

 		./largest

inputting some numbers, and (on a blank line) after the data send a End-Of_Transmission signal: hold down the Control key and tapping the letter D.

Make sure it handles missing data and a series of numbers.

Otherwise fix it!

Modifying the program

Make a copy of largest.cpp called smallest.cpp

 		cp largest.cpp smallest.cpp

(or use the GUI Konqueror)

Change smallest.cpp so that it outputs the smallest of the input numbers rather than the largest.

If...

Create a new file called "grade.cpp" containing this code (do not use copy/paste!):

 /* Programmers: Kay Zemoudeh & Dick Botting

    Program Name:    grade.cpp

    This program translates a percentage grade into a letter grade

    or else reports an error.

 */

 #include <iostream>

 #include <string>

 using namespace std;

 int main()

 {

    double percentage;

    cout <<"Enter a percentage (0..100): ";

    cin >> percentage;

    cout << "Letter grade is ";

    if (percentage > 100)

    {

       cout << "Percentage too large";

       return 2; /* signals error #2 to operating system*/

    }

    else if (percentage >=95)

       cout << "A";

    else if (percentage >= 85)

       cout << "B";

    else if (percentage >=75)

       cout << "C";

    else if (percentage >=65)

       cout << "D";

    else if (percentage > 0)

       cout << "F";

    else

    {

      cout << "Invalid Percentage: " << percentage << endl;

       return 1;/* to signal an error to the operating system*/

    }

    cout << endl;

    return 0;

 } // main

Don't forget to save it.

Check your file

If you can spot any errors, correct them.

Compile and run the program

Make sure there are no syntax, semantic, or logic errors. Here is a suitable command

 		c++ -o grade grade.cpp

Are any compile errors output? If not go to the next step.

Test your grading program

Try every grade in turn... and some bad data. Does the program do the right thing? If not, figure out why and fixit.

Programming Exercise

Modify the program grade.cpp to also handle letter grades followed by + or -. make the code match the grading in the syllabus [ ../../syllabus.html#grading ]

(Hint: Try to minimize your changes.)

(Hint: Start by writing some examples of what you want by hand. Then it often helps to draw a picture of how a program behaves or to describe the inputs and what happens to them. Then work on the source code. )

First fix the syntax errors.

Then test with as many test inputs that you can think of. Make sure your program is error free.

Getting this far by the end of the lab gets you an A for the lab.

To earn credit

Either show the lab instructor the programs or print them and hand the printouts in.

Authors

Who	When	What
Kay Zemoudeh	12/9/1997	Author
Dick Botting	04/21/2005	Improved
Dick Botting	01/22/2008	Rewrote

. . . . . . . . . ( end of section CSci201 Laboratory 04 -- decisions and loops) <<Contents | End>>

Abreviations