lecture 4: computer languages. a tutorial introduction to c++ cos120 software development using c++...
TRANSCRIPT
Lecture 4: Computer Languages.A Tutorial Introduction to C++
COS120 Software Development Using C++ AUBG, COS dept
2
Lecture Contents:
Programming languages (Reminder, may skip); Processing HLL program (Reminder, may skip);
– (Editing, Compiling, Linking, Loading, Running) The C++ Programming Language
– A tutorial introduction.
3
Programming Languages
Machine Language– “Native tongue” of the computer– Binary 0s and 1s that specify what to do
• 0010 0000 0000 0100• 1000 0000 0000 0101• 0011 0000 0000 0110
High - Level Languages– Resemble human language (C++, C, Pascal)
• cost = price + tax;
4
Processing a High-Level Language Program
Set of programs used to develop software encapsulated within a software package, IDE
Text editor Compiler Linker Loader Examples: MS Visual Studio, Code::Blocks, g++.
5
Processing a Program Editor used to enter the source program
– Output saved as a source file (prog.c or prog.cpp) Compiler translates the source program
– Displays syntax errors (not descriptive)– Generates an object program (prog.obj)
Linker combines object file with other object files– Generates an executable program (prog.exe)
Loader loads executable program into RAM Program execution starts Program execution terminates
6
Process Cycle
7
Tutorial Introduction to C++
Logical Structure of a program – C++ program consists of – functions and– global variables.
Functions are separate program units and contain statements that specify computing operations to be done.
Variables store values used during computation. Variables are named by the developer. Functions are named by the developer except one that is
always present and named main().
8
Tutorial Introduction to C++
Program as Top-Down hierarchy of syntax categories:– Program // Program has function(s)– Function(s) // Function has statement(s)– Statement(s) // Statement has expression(s)– Expression(s)// Expression has operator(s) and operand(s)– Operator(s)– Operand(s) – Data
9
Tutorial Introduction to C++
Program as Bottom-Up hierarchy of syntax categories:– Program– Function(s) // Function(s) are part of a program– Statement(s) // Statement(s) are part of a function – Expression(s)// Expression(s) are part of a statement – Operator(s) // Operator(s) are part of an expression– Operand(s) // Operand(s) are part of an expression– Data
10
Typical structure of an elementary program
<preprocessor directives>
void main()
{
<definition/declaration statements>
<executable statements>
}
Open next slide to look at the “Hello, World!” program
11
The “Hello, World!” program
C++ notation
#include <iostream>
using namespace std;
void main( )
{
cout << “\nHello, World!”;
}
12
Tutorial Introduction to C++
Names – strings of characters of any length
– case sensitive
– key words are reserved Names, also called identifiers:
– reserved words (if, else, for, while, …)
– standard identifiers (cin, cout, …)
– user defined identifiers (Price, Pom12a, FileSize, Counter, Ion12bcd, …)
13
Tutorial Introduction to C++
Data – classification by category:
– Literal Values
– Named Constants
– Variables
14
Tutorial Introduction to C++
Data – classification by type:
– Boolean (keyword bool)– Character (keyword char)– Integer (keywords int, unsigned, short, long)– Real (keywords float, double, long double)
15
Tutorial Introduction to C++
Operators: Survey on arithmetic, relational, logical and assignment operators.– Arithmetic * / %
– + -
– Relational < <= > >=
– Equality == !=
– Logical AND (conjunction) &&
– Logical OR (disjunction) ||
– Assignment =
16
Tutorial Introduction to C++
Expressions - are composed of operands and operators;
1 + 2
A – 3 * 5.6
A = B + C
A = B = 1 + 2
A = (B = C / (D*E)) + F;
Attention: expression terminated by ; is a statement
Attention: A program is a sequence of statements
17
Tutorial Introduction to C++
Executable statements: assignment
<var> = <expression>;
x = 5;
How to read? “x becomes 5” or
“x gets 5” or
“x takes the value of 5” but never
x equals 5 (NO!)
18
Tutorial Introduction to C++
Executable statements: selection/decision
if ( <expression>) <statement>
if ( <expression>) <statement1> else <statement2>
switch statement
19
Tutorial Introduction to C++
Example: fragment of linear equation solutionif ( <expression>) <statement>
if ( b != 0 ) x = -c/b;
if ( b != 0 ){ x = -c/b; cout << “\n Solution is =“ << x;
}
20
Tutorial Introduction to C++
Example: fragment of triangle area problemif ( <expression>) <statement1> else <statement2>
if ( a+b>c && b+c>a && a+c>b) { p = (a+b+c)/2; s = sqrt( p*(p-a)*(p-b)*(p-c) ); cout << “\n Area is = “ << s;
} else cout << “\nYou entered invalid data“;
21
Tutorial Introduction to C++
Example: Fragment of menu choice program switch statement
int choice; cin >> choice;switch (choice){ case 1: Rectangle(); break; case 2: Square(); break; case 3: Triangle(); break; case 4: Circle(); break; default: cout << “\n Invalid input”;};
22
Tutorial Introduction to C++
Executable statements: iteration/repetition
– for (<exp1>;<exp2>;<exp3>) <stmt>
– while ( <exp> ) <stmt>
– do <stmt> while( <exp> );
23
Tutorial Introduction to C++
Example: sum of first five integers s=1+2+3+4+5– for (<exp1>;<exp2>;<exp3>) <stmt>
int I, s=0; for ( I=1; I<=5; I++ ) {
s = s + I;// display intermediate resultscout << ‘\n’ << s;
} // display final result cout << “\n\n\nFinal sum is = ” << s;
24
Tutorial Introduction to C++ Example: sum of first five integers s=1+2+3+4+5 while ( <exp> ) <stmt>
int I = 1, s; s=0; while ( I<=5 ) {s = s + I;
// display intermediate results cout << ‘\n’ << s; I = I + 1; }
// display final result cout << “\n\n\nFinal sum is = ” << s;
25
Tutorial Introduction to C++
Example: sum of first five integers s=1+2+3+4+5 do <stmt> while( <exp> );
int I = 1; int s = 0; do { s = s + I;
// display intermediate results cout << ‘\n’ << s; I = I + 1;
} while (I<5); // display final result cout << “\n\n\nFinal sum is = ” << s;
26
Tutorial Introduction to C++
Elementary standard input/output: I/O - C notation based on library functionsgetchar(), putchar() - Read/Write a charactergets(), puts() - Read/Write a string of charsscanf(), printf() - formatted Read/Write
I/O - C++ notation based on OO streamscin - standard input stream cout - standard output stream
27
The “Hello, World!” program
C notation
#include <stdio.h>
void main( )
{
printf(“\nHello, World!”);
}
28
The “Hello, World!” program
C++ notation
#include <iostream>
using namespace std;
void main( )
{
cout << “\nHello, World!”;
}
29
The “Hello, World!” program
#include <iostream>In C++, a stream is a sequence of characters associated with
an input device, or an output device, or a disk file.Class iostream defines object cin as the stream
associated with input device (keyboard).Class iostream defines object cout as the stream
associated with output device (screen).Class iostream also defines:
– input operator >> (extract from input stream);– output operator << (insert to output stream).
30
The “Hello, World!” program
Concrete form: using namespace std;
Abstract form: using namespace <region>;
This line indicates that the program uses objects defined in the namespace specified by <region> in general (std for concrete).
This line should always follow the #include-s.
31
Before lecture end
Lecture:A Tutorial Introduction to C++
More to read:Friedman/Koffman, Chapter 02
Or Coming approx. 60 slides
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Chapter 2: Overview of C++
Problem Solving,
Abstraction, and Design using C++ 5e
by Frank L. Friedman and Elliot B. Koffman
33Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
C++ Background
• Introduced by Bjarne Stroustrup of AT&T’s Bell Laboratories in mid-1980’s
• Based on C
• Supports object-oriented programming
• 1998 Standard
34Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
2.1 C++ Language Elements
• Comments
• Compiler directives
• Function main
• Declaration statements
• Executable statements
35Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Comments
• // symbols indicate a line comment - apply to just the rest of the line
• Block comments start with /* and end with */ - apply to as many lines as you like
• Used to describe the code in English or provide non-code information
• E.g. to include the name of the program or the author’s name
36Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Listing 2.1 Converting miles to kilometers
37Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
#include <filename>
• Compiler directive
• Includes previously written code from a library into your program
• E.g.
#include <iostream>
has operators for performing input and output within the program
• Libraries allow for code reuse
38Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
using namespace std;
• Indicates to compiler that this program uses objects defined by a standard namespace called std.
• Ends with a semicolon
• Follows #include directives in the code
• Must appear in all programs
39Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Function main
int main ( )
{
// function body
}
40Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Function main
• Exactly one main function per program
• A function is a collection of related statements that perform a specific operation
• int indicates the return type of the function
• ( ) indicates no special information passed to the function by the operating system
41Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Types of Statements
• Declaration statements - describe the data the function needs:
const float KM_PER_MILE = 1.609;
float miles,
kms;
• Executable statements - specify the actions the program will take:
cout << “Enter the distance in miles: “;
cin >> miles;
42Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
2.2 Reserved Words (Keywords)
• Have special meaning in C++
• Cannot be used for other purposes
43Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Table 2.1 Reserved words in Listing 2.1
44Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Identifiers
• Names for data and objects to be manipulated by the program
• Must begin with a letter or underscore (not recommended)
• Consist only of letters, digits, and underscores
• Cannot be reserved word
• Upper and lower case significant
45Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Identifiers
Identifier Usecin C++ name for standard input stream
cout C++ name for standard output stream
km Data element for storing distance in kms
KM_PER_MILE Conversion constant
miles Data element for storing distance in miles
std C++ name for the standard namespace
46Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
2.3 Data Types
• Defines a set of values and operations that can be performed on those values
• integers– positive and negative whole numbers,
e.g. 5, -52, 343222– short, int, long– represented internally in binary– predefined constants INT_MIN and INT_MAX
47Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Data Types (con’t)
• Floating point (real)– number has two parts, integral and fractional– e.g. 2.5, 3.66666666, -.000034, 5.0– float, double, long double– stored internally in binary as mantissa and
exponent– 10.0 and 10 are stored differently in memory
48Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Data Types (con’t)
• Boolean– named for George Boole– represent conditional values– values: true and false
49Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Data Types (con’t)
• Characters– represent individual character values
E.g. ’A’ ’a’ ’2’ ’*’ ’”’ ’ ’– stored in 1 byte of memory– special characters: escape sequences
E.g. ’\n’ ’\b’ ’\r’ ’\t’ ‘\’’
50Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
string Class
• Strings not built-in, but come from library
• Classes extend C++
• string literal enclosed in double quotes
E.g.: “Enter speed: “ “ABC” “B” “true”
“1234”
• #include <string>– for using string identifiers, but not needed for
literals
51Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Variable Declarations
• Set aside memory with a specific name for the data and define its values and operations
• The value can change during execution
• type identifier-list;
• E.g.: float x, y;
int me, you;
float week = 40.0;
string flower = “rose”;
52Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Constant Declarations
• Memory cells whose values cannot change once set
• const type constant-identifier = value;
• E.g.:
const float KM_PER_MILE = 1.609;
• Often identified by using all upper case name
53Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Listing 2.2 Printing a welcoming message
54Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
2.4 Executable Statements
• Assignment statements
• Input statements
• Program output
• The return statement
55Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Figure 2.2 Memory (a) before and (b) after execution of a program
56Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Assignment Statements
• variable = expression;
• E.g.:
kms = KM_PER_MILE * miles;
57Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Input Statements
• Obtain data for program to use - different each time program executes
• Standard stream library iostream
• cin - name of stream associated with standard input device (keyboard by default)
• Extraction operator (>>)
• E.g.:cin >> miles;
cin >> age >> firstInitial;
58Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
In Listing 2.2:
cin >> letter1 >> letter2 >> lastname;
has the effect:
59Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Figure 2.6 Effect of cin >> letter1 >> letter2 >> lastname;
60Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Program Output
• Used to display results of program
• Also standard stream library iostream
• cout - name of stream associated with standard output device (monitor by default)
• Insertion operator (<<) for each element
cout << data-element;
61Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Program Output
• cout statement can be broken across lines
• Strings cannot be broken across lines
• Prompt messages used to inform program user to enter data
• Screen cursor is a moving marker indicating the position of where the next character will be displayed
• endl (or ‘\n’) causes a new line in output
62Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Output Example
cout << “The distance in kilometers is “
<< kms << endl;
If variable kms has value 16.09, the output is:
The distance in kilometers is 16.09
63Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
The return Statement
• Last line of main function is typically
return 0;
• This transfers control from the program to the operating system, indicating that no error has occurred
64Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Listing 2.3 General Form of a C++ Program
65Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Program Style
• Use of spacing– one statement per line– blanks after comma, around operators– in between some lines of code for readability
• Use of comments– header section– document algorithm steps– describe difficult code
66Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Program Style
• Naming conventions for identifiers– Variables in all lower case, with initial capital
letter for additional words. No underscore.– Constants in all upper case, with underscores
between words.
67Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
2.6 Arithmetic Expressions
• int data type
+ - * / %
• Integer division examples - result is integer15 / 3 = 5
15 / 2 = 7
0 / 15 = 0
15 / 0 undefined
68Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Modulus for Integers
• Used only with integers
• Yields remainder - the result is integer
• Examples:7 % 2 = 1
299 % 100 = 99
49 % 5 = 4
15 % 0 undefined
15 % -7 system dependent
69Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Mixed-type Expressions
• E.g.: 4.6 / 2 evaluates to 2.3
• Rule: when an integer and a floating point operand are combined by an operator, the integer gets converted to the floating point type
• Caveat: this rule is dependent on operator precedence rules
70Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Mixed-type Assignments
• If the variable on left side of assignment is of different type than the type of the evaluated expression on the right side of =, the result of the expression must be converted to the appropriate type
71Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Mixed-type Assignment Examples
float a, b, x;
int m, n;
a=10; // result is 10.0 stored in a
b = 3.5;
m=5;
n = 10;
x = m / n; // result is 0 assigned to x
m = b * 3; // result is 10 assigned to m
72Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Order of Operator Precedence
( ) nested expressions evaluated
inside outunary +, -*, /, %binary +, -
Highest
Lowest
Associativity
Warning: watch out for the types of operands and the type of the result from evaluating each operand!
73Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Figure 2.10 Evaluation forz - (a +b / 2) + w * -y
74Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Figure 2.11 Evaluation tree form = x + k / 2;
75Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Mathematical Formulas in C++
76Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Case Study: Coin Collection
• Problem statementSaving nickels and pennies and want to exchange
these coins at the bank so need to know the value of coins in dollars and cents.
• Analysis– Need to count of nickels and pennies separately– Determine total value in cents– Use integer division by 100 to calculate dollars– Use modulus (%) to get remaining cents
77Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Case Study: Data Requirements
• Problem input– string name– integer nickels– integer pennies
• Problem output– integer dollars– integer change
• Additional program variables– integer totalCents
78Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Case Study: Formulas
• One dollar equals 100 pennies
• One nickel equals 5 pennies
79Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Case Study: Design - Algorithm
1. Read in your niece’s first name
2. Read in the count of nickels and pennies
3. Compute the total value in cents
4. Find the value in dollars and loose change.
5. Display the value in dollars and loose change.
80Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Case Study: Design - Algorithm
1. Read in your niece’s first name
2. Read in the count of nickels and pennies
3. Compute the total value in cents
3.1 totalCents is 5 times nickels plus pennies
4. Find the value in dollars and loose change.
4.1 dollars is integer quotient of totalCents and 100
4.2 change is integer remainer of totalCents and 100
5. Display the value in dollars and loose change.
81Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Case Study: Implementation
• / used to implement step 4.1
• % used to implement step 4.2
• Verify that correct data types are used
• Verify mixed-type operations and promotions
82Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Case Study: Testing
• Test results using various input combinations
• Verify results by hand or with calculator
83Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Listing 2.4 Value of a coin collection
// File: coins.cpp
// Determines the value of a coin collection
#include <iostream>
#include <string>
using namespace std;
int main()
{
string name; // input: niece’s first name
int pennies; // input: count of pennies
int nickels; // input: count of nickels
int dollars; // output: value of coins in dollars
int change; // output: value of coins in cents
int totalCents; // total cents represented
84Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
// Read in your niece’s first name.
cout << "Enter your first name: ";
cin >> name;
// Read in the count of nickels and pennies.
cout << "Enter the number of nickels: ";
cin >> nickels;
cout << "Enter the number of pennies: ";
cin >> pennies;
Listing 2.4 Value of a coin collection (continued)
85Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
// Compute the total value in cents.
totalCents = 5 * nickels + pennies;
// Find the value in dollars and change.
dollars = totalCents / 100; // integer division
change = totalCents % 100;
// Display the value in dollars and change.
cout << "Good work " << name << '!' << endl;
cout << "Your collection is worth "
<< dollars << " dollars and "
<< change << " cents." << endl;
return 0;
}
Listing 2.4 Value of a coin collection (continued)
86Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
coins.cpp Sample Execution
Enter your first name: Sally
Enter the number of nickels: 30
Enter the number of pennies: 77
Good work Sally!
Your collection is worth 2 dollars and 27 cents.
87Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
2.7 Interactive Mode, Batch Mode, and Data Files
• Interactive mode - input from user via keyboard
• Batch mode - input via a file, no user interaction
• Input/output redirection can be used for batch mode
88Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Input Redirection• Requires a file already containing all input
data before the program is executed• At the time the program is executed, the
input file is specified• E.g. in UNIX
metric < mydata• Executes the program metric using the file
mydata for input• Echo printing often used with batch input
89Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Output Redirection• Sends ALL output to a file instead of to the
display monitor• Not typically used with interactive input mode,
since even prompt messages will be sent to the output file
• E.g. in UNIX (not typical)
metric > myoutput• Both input AND output redirection
metric < mydata > myoutput
90Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
2.8 Common Programming Errors
• Syntax– a grammatical error in the formation of a
program statement– detected by the compiler– prevents translation of source code into object
code, so no execution possible– messages are compiler dependent, so you must
learn how your compiler identifiers errors
91Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Common Programming Errors
• Run-time errors– detected and displayed during execution of a
program– usually fatal - halts execution of code
92Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Common Programming Errors
• Undetected errors– program runs to completion, but results are
incorrect– often the result of input of the wrong type being
entered
93Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Common Programming Errors
• Logic errors– caused by a faulty algorithm– often difficult to locate– can result in either a run-time or undetected
error– system cannot identify - up to programmer to
locate– vital to verify program output to ensure correct
results
94
Thank You
For
Your Attention!