Fundamental Data Types

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)

Consider the following simple problem:
I have 8 pennies, 4 dimes, and 3 quarters in my purse. What is the total value of the coins?

[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.

Syntax 2.1: Output Statement

cout << expression₁ << expressioun₂ << ... << expression_n;

Example:	cout << pennies; cout << "Total value = " << total << "\n";
Purpose:	Prints the values of one or more expressions.

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.

Syntax 2.2: Comments

/* comment text */
// comment text

Example:	/* total value of coins */ // total value of coins
Purpose:	Add a comment to help the human reader understand the program.

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)

Syntax 2.3: Variable Definition Statement

type_name variable_name;
type_name variable_name = initial_value;

Example:	int pennies = 8; double total;
Purpose:	Defines a new variable of a particular type, and optionally supply an initial value.

Input and Output (coins2.cpp)

The program could ask how many coins I have of any kind, and then compute the total.

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]

Syntax 2.4: Input Statement

cin >> variable₁ >> variable₂ >> ... >> variable_n;

Example:	cin >> pennies; cin >> first >> middle >> last;
Purpose:	Read the value for one or more variables in from the console.

Assignment (coins3.cpp)

Let us compute the value of the coins by keeping a running total.

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.

Syntax 2.5: Assignment

variable = expression;

Example:	total = pennies * 0.01;
Purpose:	Store the value of an expression in a variable.

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)

Syntax 2.7: Constant Definition

const type_name constant_name = initial_value;

Example:	const double LITER_PER_OZ = 0.029586
Purpose:	Define a new constant of a particular type and supply its value.

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)

Syntax 2.8: Function Call

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

Example:	sqrt(x) pow(z + y, n)
Purpose:	The result of calling a function and supplying the values for the function parameters.

Arithmetic (cmath Library Functions)

Function

Description

sqrt(x)

square root of x

pow(x, y)

x^y

sin(x)

sine of x (in radians)

cos(x)

cosine of x (in radians)

tan(x)

tangent of x (in radians)

exp(x)

e^x

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

Syntax 2.9: Member Function Call

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

Example:	name.length() name.substr(0, n - 1)
Purpose:	The result of calling a function and supplying the values for the function parameters.

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):

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

Function	Description
`sqrt(x)`	square root of x
`pow(x, y)`	x^y
`sin(x)`	sine of x (in radians)
`cos(x)`	cosine of x (in radians)
`tan(x)`	tangent of x (in radians)
`exp(x)`	e^x
`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\|

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`