1. Course websites CS201 page link at my website: Lecture slides
Lecture slides
Assistant’s Information
Recitations
Office Hours
Make-up Rules
Plagiarism

2. Chapter 2 Writing and Reading C++ Programs
A programming language has syntax and semantics like any natural language
Syntax is the set of rules like spelling and grammar in natural languages
English: “syntax” spelled, sentences start with subject followed by verb
C++: “main” spelled, programs start with main() followed by {
Semantics is the meaning
English: “water” means H2O
C++: “int” means integer, “+” means add
Approaches of learning programming languages
Template based
Examine example programs and make analogies
Like a child learns how to speak
First learn syntax and semantics, then start by writing small programs, ...
Like learning a foreign language
Which one do you prefer? We will follow the second method
To learn to write programs, you must write programs and you must read programs.
The difference between natural language and programming languages is that even though the syntax of a sentence is wrong, the semantics could still be understood roughly. But a program will not even compile if the syntax is not right.

3. First C++ Program “Hello world” program #include <iostream>
using namespace std;
/* traditional first program */
int main() {
cout << "Hello world" << endl; // display
return 0; }
This program must be
Typed and saved in a file <name>.cpp (hello.cpp)
Compiled (syntax checked): hello.cpp  hello.obj
Linked (combined with iostream library) : hello.obj  hello.exe
Run (execute) hello.exe

4. Format of a C++ Program
#include <iostream>
using namespace std;
/* traditional first program */
int main() {
cout << "Hello world"
<< endl; // display
return 0; }
#include statements comment int main() { C++ statement 0; comment C++ statement 1; … C++ statement (n-1); }

5. Format of a C++ Program using namespace std;
#include statements make libraries of classes and functions available to the program
Utility functions and tools that make the programmer’s life easier are defined in libraries
Helps programmers develop code independently in a standard way and reuse common operations
Compiler needs access to interface (definition), what the functions look like, but not to the implementation of those functions
This is in the #included file
e.g. #include <iostream>
for input/output functions
all programs that use standard C++ libraries should have
using namespace std;

6. Format of a C++ Program
Comments make programs readable by humans (and by assistants!)
Easier maintenance
Try to use natural language, do not repeat the code!
Bad example
area = pi * r * r; /* area is pi*r*r */
Better example
area = pi * r * r; /* calculate area */
Best example
area = pi * r * r; /* calculate area of a circle of radius r */
Two ways of commenting
Using // make the rest of the line comment
area = pi * r * r; // calculate area
Between /* and */ /*
Calculate area of a circle of radius r */
area = pi * r * r;
Compiler disregards comments
Comments in your homework affect your grades
In VC++, comments are in green

7. Format of a C++ Program Execution of the program begins with main
Each program must have a main function
Execution of C++ programs is organized as a sequence of statements
Statements execute sequentially one after another
statement 0, statement 1, …, statement (n-1)
Branching, repetition are possible (we will see them later)
The main function returns a value to the operating system or the environment in which it is executed
return 0
Why 0? Because 0 means no problems (errors) encountered!

8. Format of a C++ Program Each statement ends with a “;” (semicolon)
except #include and function headers like main()
Each statement has optional line break after the “;”
int main() {
// This is valid code too
cout << "Hello world" << endl; return 0; }
Blanks (spaces) are optional but makes code much more readable (we will see its rules)
cout<<"Hello world"<<endl;

9. Rules of C++ Now some syntax rules and definitions ABC of C++
What is a “literal”?
Reserved words (“keywords”)
What is an “identifier”?
Variables and basic types
Symbols and compound symbols
Where to use blanks, line breaks?
Basic Input/Output

10. Literals Fixed (constant) values They can be output by cout
They cannot be changed during program’s execution
They can be output by cout
Different format for different types:
String literals
Sequences of characters
Within double quotes (quotes are not part of the string)
Almost any character is fine (letters, digits, symbols)
"Hello world!"
" 10 > 22 $&*%? "
Numeric literals
Integer
Real e3
1.2334e3 is times 10 to the power 3 (scientific notation)

11. Identifiers Names of programmer defined elements in a program
Names of variables, functions and parameters
Examples:
number1 valid
number_1 valid
mySum valid
my_sum_1 valid
1number not valid
Syntax (rules):
Sequence of letters (a .. z, A ..Z), digits (0 ..9) or underscore
Cannot start with a digit
Case sensitive (number1 and Number1 are not the same)
Pick meaningful names to improve readability and understandability of your program (be consistent)
Hungarian notation

12. Reserved Words (Keywords)
Special and fixed meanings
built-in in C++ language
no need to have libraries to use them
You cannot use a reserved word as a user-defined identifier
Cannot be changed by programmer
int
return
Full list is Table 2.1 of the textbook
Full list also in MSDN:
In MS VC++, reserved words are automatically blue

13. Variables and Types
Variables are used to store data values that can change during the program
Input (cin) data is stored in variables
Results are stored in variables
Named memory locations of certain sizes
Must be defined before they can be used
Often initialized before use
Syntax:
type name; identifier
type name1, name2, …, namek;
Common types:
int number1, age, sum;
string myName, last_name;
float area, distance;
Memory
number1
age
sum
myName
last_name
area
distance

14. Symbols Non-digit and non-letter characters with special meanings
Mostly used as operators (some examples below, full list later)
Symbol
Meaning
Example +
addition, sign
12 + 2, +67 -
subtraction, minus
37 – 5, -8 *
multiplication
3 * 5 * number /
division
5.2 / 1.5 %
modulus/remainder
7 % 2 =
assignment
sum = x + 5;
Compound symbols (two consecutive symbols – one meaning),
examples below, full list later
Symbol
Meaning
Example /*
comment start
/* calculates */
comment end
area */
<<
stream output
cout << "Hello";
>>
stream input
cin >> number; ==
equality comparison
number == 0

15. Arithmetic Operations
Operators: * / %
Operands: values that operator combines
variables or literals
Combination of operators and operands is called expression
Syntax and semantics for arithmetic operations:
Addition
Subtraction
Multiplication
Division
Modulus
23 + 4
23 * 4
21 / 4 is 5
21 % 4 is 1
x + y
x * 3.0
21 / 4.0 is 5.25
18 % 2 is 0
d –
d * 23.1 * 4
x / 4
x % 4
5 – 3 * 2
x / y
x % y
Talk about the result of the operations in red in the table
See Figure 3.4 in the book.

16. Assignment Operator Stores a new value in a variable
variable = expression;
The value of expression becomes the value of variable
int number;
number = 40;
number = number + 5;
string name;
name = "Gulsen";
number * 4 = 56; wrong syntax
Previous value of variable is lost
Be careful about the types of left and right hand sides
they must match
compiler may or may not warn you
int a = 32.6;
Memory
number
name 45
value
name
Gulsen

17. Example Program Write a program to calculate the area of a circle
program first input a name and print a greeting
input the radius
calculate and display area
identify literals, identifiers, keywords, symbols, variables and expressions
#include <iostream>
#include <string>
using namespace std;
// area calculation program
int main() {
int radius;
float area;
string myname;
cout << "Please enter your name: ";
cin >> myname;
cout << "Hello " << myname
<< "! Welcome to my area calculation program" << endl;
cout << "Please enter the radius of your circle: ";
cin >> radius;
area = 3.14 * radius * radius;
cout << "the area is: " << area << endl;
return 0; }

18. Issues with the Example Program
What happens if the user enters a real number for radius?
wrong result
solution: real radius
Can we combine?
cout << "Hello " << myname
<< "! Welcome to my area calculation program" << endl;
cout << "Please enter the radius of your circle: ";
Can we eliminate the variable area?
area = 3.14 * radius * radius;
cout << "the area is: " << area << endl;

19. Where to use Blanks (Newline)
You must have at least one blank
between two words (identifiers or keywords)
e.g. int number;
between a word and numeric literal
e.g. return 0;
You cannot have a blank
within a word (e.g. float)
within a compound symbol (e.g. <<)
within a literal (e.g )
except string literals, in string literals blanks are blanks
At all other places
blanks are optional and increases readability
area = 3.14*radius * radius;
Several blanks are functionally same as single blank
except within string literals (e.g. "Hello world")
Newlines can be used whenever blank can be used

20. Stream Output Output is necessary for our programs
Standard output stream cout is the monitor (read “see-out”)
cout is implemented in the iostream library
Output is sent to stream by the << operator
cout << "Hello world! ";
What can be output?
String literals between " ", expressions and variables
More than one output could be sent to the stream
cout << "Hello" << " world!" << endl;
endl means “end of line”
causes next output to be displayed in next line
cout << "Hello world" << endl << " and universe" << endl;
int sum = ;
cout << "sum = " << sum << endl;
cout << 45 << " km. = ";
cout << 45 * 0.62 << " miles"
<< endl;
Hello world
and universe
sum = 12
45 km. = 27.9 miles

21. Stream Input Input is also necessary for our programs
Standard input stream cin is the keyboard (read “see-in”)
cin is also implemented in the iostream library
You can input only to variables
Input is read from the stream by the >> operator
cin >> number;
More than one input could be read from the stream
cin >> variable1 >> variable2 >> variable3 … ;
Data will be read into the variables in the same order they are in the cin statement
int a, b, anynumber;
cin >> b >> anynumber >> a;
first the value for b, then the value for anynumber, then the value of a must be entered by the user using the keyboard

22. Stream Input
You have to have at least one blank between any two input entry
Multiple blanks are OK
You may input values at several lines for a single cin statement
You cannot display something using cin statement
Type match between variable and the corresponding input value
If mismatch then the input entry fails for the rest of the program
But the values read up to that point are kept in the variables