Chapter 2: Fundamental Data Types

Lecture Goals

• To understand integer and floating point numbers
• To write arithmetic expressions in C++
• To appreciate the importance of comments and good code layout
• To be able to define and initialize variables and constants
• To be able to change the values of variables through assignment
• To use the standard C++ string type to define and manipulate character strings
• To be able to write simple programs that read numbers and text, process the input, and display the results

Number Types (coins1.cpp)

• [d]
  
• Integer numbers (int) are whole numbers without a fractional part.
  • Includes zero and negative numbers
  • Used for storing values that are conceptually whole numbers (e.g. coins)
  • Processed faster and require less storage space (than floating point numbers)
    
• Floating-point numbers (double) have decimal points (in US standard).
  • Floating-point numbers are 1.2; 0.001; -0.12; 1e-2; 13E2; -2.9e-2; etc.

cout << expression1 << expressioun2 << ... << expressionn;

cout << pennies;
cout << "Total value = " << total << "\n";

• Use the asterisk * for multiplication (not dot or cross).
• Comments are denoted by /* comment text */ or // comment text
  • Ignored by the compiler.
  • Explains the program to other programmers or yourself.

/* comment text */
// comment text

/* total value of coins */
// total value of coins

• Variables are locations in memory that can hold values of a particular type.
• Variable naming rules (symbolic names, identifiers):
• Names must start with a letter.
• Remaining characters are letters, digits or underscore_ (no spaces or special symbols)
• You cannot use reserved words (as int, return, etc.).
• Variable names are case-sensitive (e.g. Area and area are different names).
• To avoid any possible confusion we will never use any uppercase letters in variable names.
  
• Each variable has:
  • Type (e.g. int or double)
  • Name (e.g. pennies)
  • Value (e.g. 8)

type_name variable_name;
type_name variable_name = initial_value;

int pennies = 8;
double total;

Input and Output (coins2.cpp)

• Input stream operator (>>) reads console input:

  cin >> pennies;

• The program waits for the user to type in a number and Enter key.
• The number is placed into the variable, and the program executes the next statement.
  
• If user doesn't enter appropriate input, then the stream fails (sets cin in "failed" state). All subsequent input also fails.
• [d]
• Can read multiple values:

  cin >> pennies >> nickels >> dimes >> quarters;

• User enters input separated by spaces or newlines, e.g.
  

  8 0 4 3

  or

  8
  0
  4
  3

• Input is buffered. If you type two inputs on one line, the second one is saved for the next input statement.
• [d]
  

cin >> variable1 >> variable2 >> ... >> variablen;

cin >> pennies;
cin >> first >> middle >> last;

Assignment (coins3.cpp)

Assignment (Assignment Operator)

• = operator assigns the value of the expression on the right to the variable on the left.

  total = pennies * 0.01;
  total = count * 0.05 + total;

• Compute the value of the nickel contribution, add to it the value of the running total, and place the result again into the variable (memory location) total.
  
• Do not confuse the assignment operation with algebraic equality.

variable = expression;

total = pennies * 0.01;

Assignment (Increment and Decrement)

• Assignments like month = month + 1; are very common in programming.

  

• This assignment increments the variable month.
• C++ uses a special shorthand for increment:

  month++; // add 1 to month

• C++ also supports decrement:

  month--; // subtract 1 from month

Constants (volume1.cpp)

• Giving symbolic names to constants makes programs easier to read and modify.
• Example: Suppose you switch from 2-liter bottle to half gallon bottles:
  • Must find every 2 in program.
  • Decide if number represents bottle volume, or something else.
  • Replace with 1.893 if appropriate.
• Constants mean only changing a program at one location.

Constants (volume2.cpp)

const type_name constant_name = initial_value;

const double LITER_PER_OZ = 0.029586

Arithmetic

• All four basic arithmetic operations are supported by C++:
  • Addition and subtraction: + -
  • Multiplication and division: * /
• Multiplication and division bind more strongly than addition and subtraction.
• Use parentheses to indicate the order in which the subexpressions should be evaluated.

  	a + b / 2
  	( a + b ) / 2

• In division, if at least one of the numbers is a floating-point number, the result is a floating point number:

  9.0 / 4.0   /* 2.25 */
  9 / 4.0     /* 2.25 */
  9.0 / 4     /* 2.25 */

• If both numbers are integers, then the result is an integer:

  9 / 4      /* 2 Attention! */

• To get the remainder of (integer) division between two integers, use the modulus operator %:

  9 % 4      /* 1 remainder */

Arithmetic (coins4.cpp)

function_name(expression1,expressioun2, ..., expressionn);

sqrt(x)
pow(z + y, n)

Arithmetic (cmath Library Functions)

Function	Description
sqrt(x)	square root of x
pow(x, y)	xy
sin(x)	sine of x (in radians)
cos(x)	cosine of x (in radians)
tan(x)	tangent of x (in radians)
exp(x)	ex
log(x)	(natural log) ln(x), x > 0
log10(x)	(decimal log) lg(x), x > 0
ceil(x)	smallest integer >= x
floor(x)	largest integer <= x
fabs(x)	absolute value |x|

Arithmetic (Analyzing an Expression)

Strings

• A string is a sequence of characters.
  
• To use the string type, include the header file for strings: #include<string>.
• C++ strings are enclosed in quotes, which are not part of the string.
• The string type behaves like number types with respect to declaration, assignment, output and input:

  string name = "John"; // declaration and initialization
  name = "Carl";        // assignment
  cout << name << ", please enter your name:"; // output
  cin >> name;          // input (stops at first space)

• Use the statement

  getline(cin, name);

  to read all keystrokes until the Enter key; e.g. should the user type

  Harry Hacker

Strings (Member Functions)

• The number of characters in a string is called the length of the string.
• You can compute the length of the string using the length() function.
• The length function is a member function, and must be invoked using the dot notation.

Name	Purpose
s.length()	The length of s
s.substr(i, n)	The substring of length n of s starting at index i
getline(f, s)	Read string s from the input stream f

expression.function_name(expression1,expressioun2, ..., expressionn)

name.length()
name.substr(0, n - 1)

Strings (Substrings)

• The substr(start, length) member function is used to extract substrings.

  string greeting = "Hello, World!\n";
  string sub = greeting.substr(0,4);
  /* sub is "Hell" */

• The position numbers in a string start at 0. The last character is always one less than the length of the string.

  H	e	l	l	o	,		W	o	r	l	d	!	\n
  0	1	2	3	4	5	6	7	8	9	10	11	12	13

• string w = greeting.substr(7, 5);

  H	e	l	l	o	,		W	o	r	l	d	!	\n
  0	1	2	3	4	5	6	7	8	9	10	11	12	13

Strings (Concatenation)

• The + operator concatenates two strings.

  string fname = "Harry";
  string lname = "Hacker";
  string name = fname + " " + lname;

• One or both strings surrounding the + must be a variable.

Strings (initials.cpp)

Strings (Output Formatting)

• Unformatted output:

  cout << pennies << " " << pennies * 0.01 << "\n";
  cout << nickels << " " << nickels * 0.05<< "\n";
  cout << dimes << " " << dimes * 0.1 << "\n";
  cout << quarters << " " << quarters * 0.25 << "\n";

  will produce (form1.cpp):
  

   1 0.01
   12 0.60
   4 0.40
   120 30.00

• To format output we use the manipulators accessed by including #include<iomanip>
• The setw() manipulator sets the field width of the next output.
• The setprecision() manipulator is used to set the precision of the next floating point number.
• By using the fixed manipulator, you ensure that trailing zeros are displayed.
• The sequence of commands

  cout << fixed << setprecision(2);
  cout << setw(8) << pennies << " "
       << setw(8) << pennies * 0.01 << "\n";
  cout << setw(8) << nickels << " "
       << setw(8) << nickels * 0.05<< "\n";
  cout << setw(8) << dimes << " "
       << setw(8) << dimes * 0.1 << "\n";
  cout << setw(8) << quarters << " "
       << setw(8) << quarters * 0.25 << "\n";

  creates the table (form2.cpp):

         1     0.01
        12     0.60
         4     0.40
       120    30.00