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Lab Objectives

To gain experience with

• integer and floating-point numbers
• writing arithmetic expressions in C++
• appreciating the importance of comments and good code layout
• defining and initializing variables and constants
• recognizing the limitations of the int and double types and the overflow and roundoff errors that can result
• reading user input and displaying program output
• changing the values of variables through assignment
• using the ANSI C++ standard string type to define and manipulate character strings
• writing simple programs that read numbers and text, process the input and display the results

R1. Number Types

Numbers are essential to computing. In C++ there are two fundamental numeric types: integers and floating point numbers. Integers have no decimal part, whereas floating point numbers do. Variables of either type are represented by user specified names. Space in the computer's memory is associated with the name so that the variable acts like a container for the numeric data.

Declaring a variable reserves space in memory and associates a specified name with it. When a variable is declared, it contains whatever value is leftover from the previous use of the memory space. Initializing a variable sets it to a specific value. If no specific value is known, it's a good idea to initialize new variable to zero in order to avoid having it contain a random value.

Are the following integers and floating point numbers properly declared and/or initialized? If not, supply a correction.

When declaring a variable, take a moment to consider by what name it will be known. A valid name is made up of characters from the set:

The only limitation is that a variable name can't begin with a digit. Of course, the name must be unique. Neither you nor the compiler would be able to distinguish between variables with the same name. For some simple cases, using single letters like i, j, k is enough, but as programs grow larger this becomes less informative. Like the name for a product or service, a variable name should do two things:

Mostly, this will happen if the name selected is descriptive enough to tell a human reader how a variable is being used, for example count_messages, user_preference, customer_name  This will also help you when you are trying to maintain the program later on, since a descriptive name will assist you in remembering exactly what a variable is used for.

Complete the following table of (bad) variable names, better names and descriptions.

R2. Constants

Like variables, any numeric constants used by your program should also have informative names, for example: const int FLASH_POINT_PAPER = 451; or const int BOILING_POINT_WATER = 212. Using named constants transform statements such as int y = 451 - x + 212 into the more intelligible int y = FLASH_POINT_PAPER - x + BOILING_POINT_WATER.

Give definitions for each of the constant descriptions listed below

P1. Comments

Even carefully named variables are rarely sufficient to fully convey the operation of a program. They do not, for example, provide an explanation of a future feature that could be implemented because of how something is done now, or leave a detailed description of how a variable is computed. You can however place any additional information necessary in a comment. Comments are plain text for humans to read. They are separated from the machine readable code needed by the compiler by either of:

/* say whatever you want in here, between the slash-asterisk boundaries
   the compiler will ignore it
   . . .         
*/ 

or

// say what ever you want from the double slashes to the end of the line . . .
// the compiler will ignore it
// . . .

From both design and documentation perspectives, it is a good idea to get in the habit of commenting your code as early as possible. For example, provide a brief description of what the program coins.cpp from Section 2.2 does.

#include <iostream>
using namespace std;
int main()
/* your work goes here--use // or /* as appropriate */
   
{  cout << "How many pennies do you have? ";
   int pennies;
   cin >> pennies;
   
   cout << "How many nickels do you have? ";
   int nickels;
   cin >> nickels;

   cout << "How many dimes do you have? ";
   int dimes;
   cin >> dimes;

   cout << "How many quarters do you have? ";
   int quarters;
   cin >> quarters;
   
   double total = pennies * 0.01 + nickels * 0.05
       + dimes * 0.10 + quarters * 0.25;
       /* total value of the coins */
       
   cout << "Total value = " << total << "\n";
   
   return 0;
}

Now, extend coins.cpp to prompt for and accept the number of Golden Dollar coins, placing the finished code here. Add a comment to show when you modified the code, and what change you made.

R3. Input and Output

C++ defines two standard streams that can be used for text mode input and output, respectively cin and cout. Operator >> and << are used to direct input and output to and from the stream.

In coins.cpp, for example, you used cin >> pennies; to get user input. The expression cout << "Total value = "; displays the message "Total value =". It was followed by << total , which places the contents of the variable total into the cout stream.

Items in the input stream are separated by white space - spaces, tabs and newlines. For example, two numbers may be input as

3   4

or

3
4 

If there is an error, the stream goes into a failed state rather than plodding ahead with bad data. For example, if the user has typed

l0

(with a letter l) instead of

10

then the stream fails when trying to read a number.

Do the following lines of input data work properly? Why or why not?

User Input: 24 25 26

int first, second, third;
cin >> first >> second >> third;

User Input: 24.4 25.5 26

double fourth, fifth, sixth;
cin >> fourth >> fifth >> sixth;

User Input: 24.4 25.5 26.6

int seventh, eighth, ninth;
cin >> seventh >> eighth >> ninth;

User Input: 23.4 24.5

double tenth, eleventh, twelfth;
cin >> tenth >> eleventh >> twelfth;

R4. Assignment

There are several primary ways to modify the contents of a variable in C++.

• cin >> variable; the '>>' operator places the contents of the input stream into the variable
• variable = 3; the '=' operator, called the assignment operator, takes whatever combination of values are on its right side and puts them into a variable on its left side.
• variable++; the '++' operator increments, or adds 1 to the variable to which it is appended. Similarly, the '--' operator will decrement an integer variable by 1.

During compilation, values on both sides of the >> and = operators are checked to insure that the data received matches the data type of the variable to which it will be assigned. Are the right and left hand sides of the assignment operators of compatible type in the following statements?

What error does your compiler give in these cases?:

Because a variable of any given type represents a fixed amount of space in memory, there is a limit to how large a value it can store.

Size limitations are particularly evident with integers. On some computers, integers can only be about 32,000, on others, they can go up to a little more than 2,000,000,000. What is the largest value your compiler will accept for a signed integer? What is the most negative allowed value?

Floating point numbers don't round to the nearest integer value. Can you explain the values your compiler assigns to f and g in:

double f = pow(10.0, 20.0) - 53;
double g = f;
g = g - 53;
cout << f << "\n" << g << "\n";

R5. Arithmetic

Recalling what you've learned about integers and floating point values, what value is assigned to Z by each of the following?

Translate the following algebraic expressions into C++ :

     x 
y = ---
    1-x

Strings

Many programs manipulate not just numbers but text. C++ stores text in string variables. They are declared and assigned in a manner similar to a numeric variable, and the sequence may have any length, including being uninitialized or having 0 characters. For example,

string name = "Jane Doe";

assigns the 8 characters enclosed in quotes to the variable name.

 string temp = name; 

assigns the content of variable name to variable temp

cout << name; 

displays the contents of variable name on the standard output stream.

R6. Concatenation

Given:

   string first_name = "Kenneth";
   string last_name = "Cole";
   string name;

What value will name contain after

      name = first_name + last_name;

How could the preceding be revised to give a better result?

R7. Substrings

The primary difference between strings and numeric data types is that any portion of the characters in a string variable is itself a string variable. Such a portion is called a substring.

What will be the resulting substring in the following examples? If invalid, give a corrected version of the call to substr.

P2. Extracting Substrings

Using substr and concatenation, give a program containing a sequence of commands that will extract characters from input_string = "Four score and seven years ago our fathers"  to make output_string = "carefree and no tears". Then print output_string.

P3. Reading string input

The function getline(cin, s) read a single input line into the string s. Write a program that uses getline to read input of the following exact form:

FNAME first name
MNAME middle name
LNAME last name
ADDRESS a street name and house number
CITY a city name
STATE a state abbreviation
ZIP a zip code     
ORDER_DATE the date of the order    
TOTAL_ITEMS number of items (an integer)
ORDER_TOTAL total amount of order (type double)
SHIP_DATE   date of shipment

Then print out the top part of a shipment manifest in the following form:

John Q. Public
11801 Jones Valley Ct.
Pleasant Hills, MN 66504
=====================================================================x
Order Date: 10-Oct-2001    Total Items: 10    Order Total: $100.00
Ship Date: 20-Oct-2001

P4. Formatting numbers

You use the setprecision, setw and fixed manipulators defined in the <iomanip> header to control the formatting of numbers. Write a program that calculates the interest and principal payments on a simple loan.  Your program should query the user for a percentage annual interest rate, an initial balance and monthly payment, then print out the following table:

Month Balance		Interest	Payment
    1 $ 10050.00	$  100.50	$  500.00
    2 $ 9650.5		$   96.51       $  500.00
    3 $ 9247.01		$   92.47	$  500.00
    4 $ 8839.48		$   88.39	$  500.00

Use setw to set each column width, and use fixed and setprecision to properly show dollars and cents.

Don't forget to send your answers when you're finished.