CSCI 1300 - Lecture Notes

CSCI 1300
Lecture Notes

9/2/97

C++: C++ Program
Parts of a Program

Declarations: What is Data?
C++ Data Types

Identifiers: Declaration
Named Constants
Variables
Variable Initialization

Numerical Expressions: Basic Mathematical Operations
Precedence and Associativity
Unary Operators
Other Operators
Type Conversion
Math Library
Assignment Expressions
Shortcuts
NOTES

C++

C++ Program

A list of C++ statements.

Statements executed in order.

Statements terminated with a semicolon (;).

May contain classes, functions, variables, etc.

Simplest correct program (does nothing, but is correct).

main()
{

}

Parts of a program

Comments Information for programmers about the program Not compiled: Information for programmers about the program
Not compiled

Include files Additional files to include in the program Usually contain only definitions and prototypes, not code Often system interface files: Additional files to include in the program
Usually contain only definitions and prototypes, not code
Often system interface files

Prototypes Short definitions of functions defined elsewhere.: Short definitions of functions defined elsewhere.

Class definitions Define classes used in the program Do not allocate storage - must be done separately: Define classes used in the program
Do not allocate storage - must be done separately

Global variable declarations Variables accessible to all functions in program Considered bad practice Can be used for constants used all over the program: Variables accessible to all functions in program
Considered bad practice
Can be used for constants used all over the program

Functions The parts that do something Can be called by other functions: The parts that do something
Can be called by other functions

The main() function The main part of the program Executed first Calls other functions as necessary Each C++ program must contain exactly one main() function.: The main part of the program
Executed first
Calls other functions as necessary
Each C++ program must contain exactly one main() function.

Example: Calculating volume of a sphere.

Declarations: Types of Data Objects

What is data?

Characters

Letters ('a', 'b', 'c')

Digits ('0', '1', '2')

Symbols (';', '$', '&')

Punctuation ('.', ',', '!')

Numbers

Whole numbers (1, 3000, 102456789)

Negative whole numbers (-1, -3000, -128y234)

Numbers with a decimal point (.01, 3.7, 12357.213456)

Combinations of the above

Booleans (represented as a numeric value, 0=FALSE, 1=TRUE)

Imaginary numbers (two parts: real and imaginary)

Bank accounts

Database records

...

C++ Data Types

Character Denoted with "char" Single character Used to represent a-z, A-Z, numbers, and symbols Uses 8 bits to represent 127 or 256 unique characters ASCII standard (see appendix A) Special characters '\'', '\n', '\010', etc. (see table 3.2) '3' = '\063' and 'A' = '\101' Example: char middle_initial; middle_initial = 'A';: Denoted with "char"
Single character
Used to represent a-z, A-Z, numbers, and symbols
Uses 8 bits to represent 127 or 256 unique characters
ASCII standard (see appendix A)
Special characters '\'', '\n', '\010', etc. (see table 3.2)
'3' = '\063' and 'A' = '\101'
Example:
char middle_initial;
middle_initial = 'A';

String Null terminated list of chars Denoted with "char []" Not really a fundamental data type, but used so often that people think of it as one Uses 8 bits * number of chars. Example: char name[] = "Scott Brandt"; or char name[80]; strcpy(name, "Scott Brandt");: Null terminated list of chars
Denoted with "char []"
Not really a fundamental data type, but used so often that people think of it as one
Uses 8 bits * number of chars.
Example: char name[] = "Scott Brandt";
or
char name[80];
strcpy(name, "Scott Brandt");

Integer Whole positive or negative number Denoted with "int", "short" or "short int", "long" or "long int" Positive-only denoted with "unsigned" before "int" or "short" or "long" Ints are usually 16 bits long Shorts are usually 16 bits long, <= size of int Longs are usually 32 bits long, >= size of int Exact sizes are machine dependent Example: int age; age = 32;: Whole positive or negative number
Denoted with "int", "short" or "short int", "long" or "long int"
Positive-only denoted with "unsigned" before "int" or "short" or "long"
Ints are usually 16 bits long
Shorts are usually 16 bits long, <= size of int
Longs are usually 32 bits long, >= size of int
Exact sizes are machine dependent
Example:
int age;
age = 32;

Real Denoted with "float", "double", or "long double" 32, 64, and 96 or 128 bit real values Example: float pi; pi = 3.14159;: Denoted with "float", "double", or "long double"
32, 64, and 96 or 128 bit real values
Example:
float pi;
pi = 3.14159;

Identifiers

An identifier is a name for a data object.

Should begin with a letter (a-z, A-Z)

May contain letters, digits and underscores

Should relate to the intended use of the data object

Examples:

float radius;

char first_name[5];

int time1, time2;

Case matters - radius and Radius are not the same identifier

Declarations

Tell the compiler the type and identifier for a data object

Must occur before the first use of the object.

Examples: See above

Named constants

Named data objects whose values do not (and should not)change

Declared with "const"

Used for Mathematical constants const float pi = 3.14159; const double e = 2.71828182846; Things that don't change during the execution of the program const char errorstring[] = "Fatal error";: Mathematical constants
const float pi = 3.14159;
const double e = 2.71828182846;

Things that don't change during the execution of the program
const char errorstring[] = "Fatal error";

Can be used with any other data type

Improves readability

Everyone either knows what pi is, or can find out

Fewer people know that 3.141592653589793 is pi

Improves reliability

Only defined in one place

Especially when the same constant is reused in many places throughout the program. Improves modifiability One change rather than many. Don't need to search to make sure you have found all of the places that the constant occurs.: Improves modifiability
One change rather than many.
Don't need to search to make sure you have found all of the places that the constant occurs.

Variables

Variable = Simple Data Object

Variable names are identifiers

Before using a variable, it must be declared.

This tells the compiler what type of data it will/can contain.

The type is enforced by the compiler.

Variables are associated with the memory location that stores the actual data.

Examples: All of the above

Variable Initialization

Initial values may be assigned to variables.

Examples

int i = 0, j = 0;

double foo = 23456.1235;

Numerical Expressions

Basic mathematical operations (+, -, *, /, %)

Addition (+)

Adds two numbers

Subtraction (-)

Subtracts two numbers

Multiplication (*)

Multiplies two numbers

Division (/)

Divides two numbers

Modulus (%)

Remainder of integer division

Example: 5 % 2 = 1

Type of result will be that of the greater of the two numerical types.
Examples:

3 / 2 = 1

3.0/2 = 1.5

Precedence and Associativity

Order of mathematical operations are important

Example: (3+2)*4 = 5*4 = 20 but 3+(2*4) = 3 + 8 = 11

* and / evaluated before + and -

Example: 3+2*4 evaluated as 3+(2*4)

Precendences equal => evaluate from left to right

Example: 3+2+5 = 5 + 5 = 10 and 3*2/5 = 6/5 = 1

Parentheses enforce evaluation order

Example: (3+2)*4 = 5*4 = 20

Unary operators (+, -)

-3, +17 allowed

Higher precedence than binary operators (above)

Example: 4*-3 = -12

Other operators (~, &, |, ^, <<, >>, &&, ||)

~ = negation

& = bitwise and

| = bitwise or

^ = bitwise exclusive or

<< = bitshift left

>> = bitshift right

&& = logical and

|| = logical or

See appendix C for a list of all operators and their precedences

Type conversion

A variable or value of one numeric type may be converted to another type by casting the type.

Some information may be lost if converting to a smaller type.

Example

double value = 123.456;

int int_value;

int_value = int(value); // int_value = 123

May also be done implicitly

int_value = value;

It's clearer to make it explicit

Math library

sin(x), cos(x), tan(x), asin(x), acos(x), atan(x), sinh(x), cosh(x), tanh(x), exp(x), log(x), log10(x), pow(x,y), sqrt(x), ceil(x), floor(x)

Parameters are doubles, returns doubles

Example:

double x, sqrt_of_x;

x = 4.0;

sqrt_of_x = sqrt(x); // sqrt_of_x = 2

Assignment Expressions

Assigns a value to a variable

variable = expression

The value can be a numeric constant, another variable, or the result of an expression.

Types must be compatible (e.g. you can't assign a string to a float)

Puts a value in the location associated with the variable

Examples

x = 4;

y = 3 + 7.5;

z = x * y / 4;

c = 't';

Errors

5 = x;

x + 7 = 3;

c = "ABC";

x = "123" + "456";

Returns value assigned to variable

Example

x = 5 + 4;

x = y = 5 + 4; // what is x? why?

Variable can be on both sides of "="

Example

x = 5;

x = x + 1;

Shortcuts

++x is equivalent to x = x+1;

++x evaluated before it is used

Example

x = 7;

y = ++x; // x = 8, y = 8

x++ is evaluated after it is used

Example

x = 7;

y = x++; // x = 8, y = 7

--x is equivalent to x = x-1

Works just like ++, but with subtraction instead of addition

+=, -=, *=, /=, %=

x ?= y is the same as x = x ? y

Example

x = 4;

x *= 5; // x = 20

Notes

All expressions must be terminated with a semicolon (;)

The value of a variable is undefined until is has been assigned.

A common error is to use a variable before a value has been assigned.