CSCI 201 Lab 7 -- Functions in C++

Getting ready

We're going to give you two projects to start the lab. Download a ZIP'ed copy of the Lab 7 projects and store it in the C:\FILES directory.

Go into the MS-DOS prompt and execute the following commands:

• cd c:\files
• mkdir Lab07
• cd Lab07
• pkunzip  -d  ..\lab07.zip

Plot in 2-D

• Ezwinvc50.lib -- the EzWindows library
• Main2D.cpp -- a driver program
• Funky.cpp -- the file you'll change

The driver program Main2D.cpp uses the EzWindows library to sequentially plot five functions that you will write. Use the mouse to move between functions. Press the X in the upper right corner of the window to terminate the program.

You should not modify Main2D.cpp in this lab. However, you are encouraged to look at it to learn a bit more about C++ and EzWindows.

The program you will modify is called Funky.cpp. Presently, this program contains five simple functions similar to:

float MyFuncN(const float x)
{
	return N*x ;
}

Go ahead and build and execute this project and look at its boring functions.

Your task

• 0.7 sine(6 x) + 0.2 sine(20 x)
• absolute value of x, that is,
  -x, if x is negative,
  and x, if x is positive
  
• x * sine(1/x), if x is not zero,
  0, if x is zero
• sqrt(1 - x²)
• First, set a float variable z to x.
  Go into a for-loop, and execute z = z*z 10 times.
  In a second for-loop, execute z = sqrt(z) 10 times.
  Return z as the result of your function.

Lab instructor check-off 1

Plot in 3-D

• Ezwinvc50.lib -- the EzWindows library
• Main3D.cpp -- a driver program
• Funky.cpp -- the file you'll change

The driver program Main3D.cpp will call the function you will write. It will pass two float arguments. Your function will return a float which will be used in the plot. Since we don't have 3-D holographic displays, we have to plot your function on a two dimensional screen. This is done by using the number returned by your function to choose between six different colors. The succinct explanation is that everything before the decimal point in your floating point number is discarded, and the fractional part is used to select a color from the following table:

Range	Color
.00 to .1666..	Red
.1666.. to .3333..	Yellow
.3333.. to .50	Green
.50 to .6666..	Cyan
.6666.. to .8333..	Blue
.8333.. to .00	Magenta

Go ahead and build and run the program. Then look at Main3D.cpp for details of the plotting routines.

Your modifications

float MyFuncN(const float x, const float y)
{
	return x+N*y ;
}

Your five functions for the 3D plot are:

• x² + y²
• x, if x >= y,
  y, if x < y
• 1/(x² + y²),
  Don't worry, your function will not be called when either x or y is equal to zero.
• larger of the absolute values of x and y or
  MAX(|x|, |y|)
• 0.5 floor(12 x) + 0.5 floor(12 y)

Lab instructor checkoff 2