Lab46 Wiki

This is a practical demonstration of the C++ and, by extension, C programming language. The following tutorials are intended to demonstrate practical programming methods that can help you solve real-world problems. As such, our first problem statement follows:

Write a menu driven program that will allow a user to convert between the following values:

• Degrees Fahrenheit to degrees Celcius
• Degrees Celcius to degrees Fahrenheit
• Inches to centimeters
• Centimeters to inches
• Pounds to Kilograms
• Kilograms to pounds

In keeping up with the nature of academic exploration, this demonstration will begin with a short description of the logic needed to solve this problem, as it can be helpful to solve the problem in plain English, before writing any C++ code:

• Show the user all the possible options, request that they make a choice, and wait.

This demonstration is a command line program, and in the interest of keeping it simple, we'll just write a quick number based menu … 1 for this, 2 for that … so on.

In psuedocode, it looks something like this:

print " 1. Fahrenheit to Celsius"
print " 2. Celsius to Fahrenheit"
print " 3. Inches to centimeter"
print " 4. Centimeters to inches"
print " 5. Pounds to kilograms"
print " 6. Kilograms to pounds"
print " 0. Exit"

• Get the number the user entered.

This line is pretty straight forward in psuedocode:

num option
print "Please choose an option"
get option

The num option part is simply declaring a variable named option that will hold a value that is a number. Even though numbers are represented differently given each different type (int, float, double, long…), in psuedocode, it is sufficient to simply say number…as in something that can be counted.

• Test the number the user entered against the options that we presented. So, if the user enters “1” (without the quotes), then run the Fahrenheit to Celsius conversion … if 2, then Celsius to Fahrenheit and so on.

In psuedocode, it looks like this:

if (option == 1) then

	//fahr to cels

else if (option == 2) then
 
	//cels to fahr
 
else if (option == 3) then

	// inches to centimeters

else if (option == 4)

	//centimeters to inches
	
else if (option == 5) then	

	// pounds to kilos

else if (option == 6) then

	// kilos to pounds

end if

The benefit of this method is that there's really very little need to error check the user's input. If it doesn't match one of the conditions (for example, if the user enters the letter 'A'), nothing happens, and the program exits. So, even though the menu states to press 0 for exit, anything other than 1 thru 6 will cause the program to exit.

• Depending on the user's choice, perform the calculation.

Each of our conversions has different logic.

Fahrenheit to Celsius … and back again:

	//fahr to Celsius
	num f; //temp in Fahrenheit
	num c; //temp in Celsius
 
	print "Enter the temperature in Fahrenheit: "
	get f
 
	c=(5.0/9.0)*(f-32)
 
	print f, " degrees Fahrenheit is ", c, " degrees Celsius."

	//cels to fahr
 
	num f
	num c
 
	print "Enter a temperature in Celsius: "
	get c;
 
	f=(9.0/5.0)*c+32;
 
	print c, " degrees Celsius is ", f, " degrees Fahrenheit."

Inches to centimeters and the other way around:

	// inches to centimeters
	const num IN_CONV = 2.54
	num inches

	print "Please enter a length in inches:"
	get inches
 
	num cent = inches*IN_CONV

	print inches, " inches  is ", cent, " centimeters"

	//centimeters to inches

	const num IN_CONV = 2.54
	num cent(0);
	print "Please enter a length in centimeters:"

	get cent;
 
	num inches = cent/IN_CONV
 
	print cent, " centimeters  is ", inches, " Inch(es)";

Pounds to kilos and the inverse

	// pounds to kilos

	num p //pounds
	num k //kilos

	print " Please enter a weight in pounds: "
	get p

	k = p/2.2;
 
	print p, " pounds is equal to ", k, " kilograms.";

	// kilos to pounds		

	num p //pounds
	num k //kilos

	print " Please enter a weight in kilograms: ";
	get k;

	p = k*2.2;

	print k, " kilograms is equal to ", p, " pounds.";

• Loop back to the beginning and allow the user one more shot at it.

There are several looping structures that could be used to solve this common task. However, in this case the do…while is a good choice, as it is a post test looping structure, and its body will be executed at least once. This means that we'll only have to code our menu once (rather than repeating it before and during the loop ), and we can set the condition to test inside the body of the loop.

Like this:

int input=0
boolean condition=false
do

	print "Please enter 1 to continue or 0 to exit"
	get input

	if (input == 1)
		condition=true

while(condition)

The above loop will execute at least once, prompting the user for an input. Upon testing the input, the condition is set, and immediately tested in the bottom of the do…while loop. Our do…while loop will differ slightly, as we will be testing a compound condition: while (input>0 && input<7)

The final psuedocode solution looks like this:

start
	num option;

	do{
	        print " 1. Fahrenheit to Celcius"
	        print " 2. Celcius to Fahrenheit"
	        print " 3. Inches to centimeter"
	        print " 4. Centimeters to inches"
	        print " 5. Pounds to kilograms"
	        print " 6. Kilograms to pounds"
	        print " 0. Exit"

	        print << " Choose an option: "
	        get option;
 
	        if (option == 1) then

	 		//fahr to celc

			num f; //temp in Fahrenheit
			num c; //temp in Celcius
	 
			print "Enter the temerature in Fahrenheit: "
			get f
	 
			c=(5.0/9.0)*(f-32)
 
			print f, " degrees Fahrenheit is ", c, " degrees Celcius."

		else if (option == 2) then
 
			//celc to fahr
 
			num f
			num c
 	
			print "Enter a temperature in Celcius: "
			get c;
 
			f=(9.0/5.0)*c+32;
 
			print c, " degrees celcius is ", f, " degrees fahrenheit."

		else if (option == 3) then

			// inches to centimeters
			const num IN_CONV = 2.54
			num inches

			print "Please enter a length in inches:"
			get inches
 
			num cent = inches*IN_CONV
 
			print inches, " inches  is ", cent, " centimeters"
 
		else if (option == 4)
			//centimeters to inches

			const num IN_CONV = 2.54
			num cent(0);
			print "Please enter a length in centimeters:"

			get cent;
 
			num inches = cent/IN_CONV
 
			print cent, " centimeters  is ", inches, " Inch(es)";
	
		else if (option == 5) then	
			// pounds to kilos

			num p //pounds
			num k //kilos

			print " Please enter a weight in pounds: "
			get p

			k = p/2.2;
 
			print p, " pounds is equal to ", k, " kilograms.";
 
		else if (option == 6) then
			// kilos to pounds		

			num p //pounds
			num k //kilos

			print " Please enter a weight in kilograms: ";
			get k;

			p = k*2.2;
 
			print k, " kilograms is equal to ", p, " pounds.";
 	       }
 
	}while (option>0 && option<7);
 
}

Solving the problem statement above in C++ is very similar to solving it in psuedocode. The only notable difference is syntax.

At this point, you can head over to the C++ Demonstration Code page and either download the code, or create a new file and copy and paste the code into that file. Name the file converter.cc and compile it using the instructions below … or follow along with this tutorial as we write the the program in C++.

The first lines in our demonstration program are comments. C++ compilers (and some C compilers) recognize a couple types of comments. For single line comments, simply use the escaped slash sequence and escaped asterisk sequence as follows:

/*

everything between "/*" and "*/" is a comment

*/

//this is a single line comment

a=x+b //end of line comment

The lines beginning with a hash (#) are not actually program statements. These lines are called preprocessor directives as they are directives that send instructions to the preprocessor. There are several directives that can be used, and some take arguments. One of the most commonly used directives in C++ is the #include directive. #include is essentially telling the preprocessor to include the contents of the source file (passed as and argument) as if it actually appeared in the program at that point. As follows:

#include <istream>
#include <ostream>
#include <iostream>
#include <iomanip>

• Namespaces
• int main()
• Variables and datatypes
• Standard Input/Standard Output
• Looping and Conditional Sturctures
• .cc file extension
• Tips & Tricks

Once you get the code to your shell, simply compile it using your favorite C++ compiler. For example, if you're using g++ you would issue the following command from the directory where you downloaded the files.

:~$ g++ -o converter converter.cc

Once the code is compiled, you can run the program using the command ./converter.

:~$ ./converter

Compiling the code

• Directory Structures
• Header Files
• Functions
• Switch statements
• Tips & Tricks

Compiling the code

• Custom data types
• Classes
• Return Values
• Arguments
• Tips & Tricks

• Using Make
• Tips & Tricks

• GUI With C++
• Necessary libraries
• portability??
• Tips and Tricks

The C Demonstration Code is located here. The context of the code will be explained through other demonstrations. The code page is only meant to be a repository for gathering the code in its original form.

Download the code using the links found at the download page. While you can copy and paste the code directly from the wiki text, this is method is discouraged as typos in each edit may not have passed through a compiler. Each major revision is compiled and tested before it is made available for download. The moral of the story is, use the links.

If you're downloading the code to a Windows machine, you'll want to open it in using something like wordpad.

• C Programming Demonstration Code