Chapter 2 Elements of a C program 1

Chapter 2 Elements of a C++ program 1

Review �Algorithms �describe how to solve a problem �Structured English (pseudo-code) �Programs �form that can be translated into machine instructions �high-level programming language: C++ 2

The First C++ Program 3

“Hello, world!” preprocessor directive #include <iostream> using namespace std; function using directive int main( ) { //print a sentence cout << "Hello, world!" << endl; return 0; } comment output statement 4

Function �A C++ program is a collection of one or more functions (subprograms). � Each function does some specific task in order to solve the problem. �There must be a function called main() �Execution always begins with the first statement in function main() �Any other functions in your program are subprograms and are not executed until they are called Try hello. World. America. cpp 5

returned value type Function block function name int main( ) parameters { cout << "Hello, world!" << endl; return 0; } statement return value �A block is a sequence of zero or more statements enclosed by a pair of curly braces { } �Each statement is ended by a semicolon ; �If a function does not return any value, the return value type should be void �Otherwise, there must be a return statement: �return the value �tell the computer that the function execution is done �There are some rules to name a function (identifier) �Parameters send the input to the function 6

The output statement: cout << "Hello, world!" << endl; � begins with cout � endl means “end of the line”. (same as ‘n’) � It moves the cursor to the next line of the display � It does not have to be the last thing in a cout statement � each thing (literal, variable, endl) is preceded with << (insertion operator) � Put spaces around the insertion operator � literals must be enclosed with quotation marks � A blank line can be created in output by using listing two endl statements � Blank spaces results when adding spaces between quotation marks Play with hello. World. cpp 7

The input statement: cin string name; cin >> name; cout << “Hello, “ << name << “!” << endl; � cin reads the next string you type on the keyboard and stores it into the variable name. � >> (extraction operator) can be used several times in a single input statement: string first. Name, last. Name; cin >> first. Name >> last. Name; cout << “Hello, “ << first. Name << “ “ << last. Name << “!” << endl; � the input will be divided by space or newline into multiple variable values. 8

Interactive Input/Output �Make a nice Human Computer Interface (HCI) �Prompt for input �Display the result with meaningful explanations �Make the screen look nice! Please input the student ID: 1001 The student information is as following: * first name: John * last name: Smith * major: Computer Science * email: smithj@university. edu Can you print a 3*3 blank table? 9

Comments �Comments are explanations of the program, function, statement, etc. �It is part of the documentation. �It starts with //. �In one line, anything after // is ignored by the compiler. �Another style: /* comments */ �Read the C++ Programming Ground Rules 10

Preprocessor directive #include <iostream> �Insert the contents of a file named iostream into the program. �A file whose name is in #include directive is a header file. �A preprocessor will preprocess the codes before the compiler by �inserting included header files �removing all comments. 11

Using directive using namespace std; �so that we can use cin, cout, endl, etc; �This statement should be placed before the main function, if iostream is used. 12

Identifier, Variable, Data Type 13

What is a computer? Network Input CPU Output MEMORY Storage 14

Hardware �CPU �Memory �Keyboard �Monitor �Disk �… 15

How to Store Data in Computer Bit Electronic Device On / Off Value: 1 / 0 Byte 8 bits Possible combinations 256 28 16

How to Store Data in Computer Binary Number: 10001111 27 128 26 25 2 4 23 22 21 20 0 1 1 + 23 + 2 2 + 2 1 + 2 0 +8 +4 +2 +1 Decimal Number: 143 17

How to Store Data in Computer Integers Binary Numbers Characters ASCII Unicode Float Numbers? Negative numbers? 18

How to Store Data in Computer KB 1024 Bytes 210 MB 1024 * 1024 Bytes 220 GB 1024 * 1024 Bytes 230 TB… 19

Declaration Statements string name; string first. Name, last. Name; int num = 10; Data. Type Identifier , Identifier, … ; �Variable: a memory location to store data �Variable value: the content in the location �Identifier: the symbolic name of a variable �Data Type: the type of data the variable is for �A declaration tells the compiler to allocate enough memory to hold a value of this data type and to associate the identifier with this location 20

Variables �Variables can have initial values int num 1, total = 0; �Variables can have different values cin >> num 1; num 1 = 58; total = total + num 1;

Identifier �An identifier is the name used for a data object(a variable or a constant), or for a function, in a C++ program �Beware: C++ is a case-sensitive language �Using meaningful identifiers is a good programming practice 22

Good Identifiers �An identifier must start with a letter or underscore, and be followed by zero or more letters (A-Z, a-z), digits(0 -9), or underscores � VALID age_of_dog Print. Heading tax. Rate. Y 2 K age. Of. Horse � NOT VALID (Why? ) age# 2000 Tax. Rate Age-Of-Cat �Identifiers should be meaningful!!! �BAD a bbb s_1234 23

C++ Data Types simple integral enum structured floating array struct union class char short int long bool float double long double address pointer reference 24

Numerical Data Types �On a 32 bit architecture: char: 1 byte (character) int: 2 bytes (integer) long: 4 bytes float: 4 bytes (real number) double: 8 bytes �Storage (and Range) is machine/system dependent 25

char �One Byte 01000011 What is the value of the byte? �As integer: 67 � As ASCII char: ‘C’ 26

ASCII Code Table 0 1 2 3 4 5 6 7 4 5 2 3 4 5 6 6 8 9 0 1 7 8 9 A B C D E 7 F G H I J K L M N O 8 P Q R S T U V W X Y 9 Z a b c 10 d e f ‘C’: 67 ‘Y’: 89 ‘ 9’: 57 All upper case letters together All lower case letters are together All digits 0 through 9 are together lower case = upper case + 32 27

ASCII Code Char ‘C’: ‘D’: ‘B’: ‘e’: ‘ 0’: ‘ 5’: ASCII Code 67 ? ? ? 48 ? 28

char and string // char : 1 byte // describes a letter, a digit or a special symbol char the. Char = ‘A’; // string: one byte for each char // one more byte at the end to // indicate the end // a sequence of characters string my. String = “CS 143”; What is the length of my. String? A string must be typed entirely on one line! What would happen if it’s not? 29

String Operations string course = “CS 143”; cout << course. length() << endl; cout << course. size() << endl; cout << course. substr(0, 2) << endl; 6 6 CS both string. length() and string. size() return the size of a string, that is, how many characters are contained in the string. This size does NOT consider the end byte! string. substr (pos, len) returns the substring of at most len charactors, starting at position pos of the string. The position index starts with 0! 30

C++ Data Types and Storage int num 1, num 2; int Sum; float average; num 1 4 num 2 Sum 5 9 num 1 = 4; num 2 = 5; average Sum = num 1 + num 2; average = Sum / 2. 0; char grade = ‘A’; string course. Name; course. Name = “CS 143”; 4. 5 course. Name C S 1 4 3 grade A 31

Symbolic Constant const Data. Type Identifier = Literal. Value; const int MAX_CREDIT_PER_SEMESTER = 21; const char BLANK = ‘ ‘; const string COURSE_NAME = “Programming in C++”; �The value of a constant never changes. �Why using constant? No Magic Numbers! �The identifier of a constant: �ALL UPPER CASE �separate the English words with an underscore _ �Comment your constant declarations 32

Is it OK? const string COURSE_NAME = “Programming in C++”; . . . cin >> COURSE_NAME; //Is it OK? COURSE_NAME = “CS 143”; //Is it OK? The values of constants CANNOT be changed! Note: in Hi. C, string constant is not supported! 33

Summary �function �input/output �comment �#include �data type �variable �identifier �constant �declaration 34