Computer Programming Basics Assistant Professor Jeon, Seokhee Assistant Professor Department of Computer Engineering, Kyung Hee University, Korea

Pre-compiler directive Opening brace Closing brace Opening brace Closing brace Structure of a C++ Program

Without namespace Hello World! Namespace std contains all the classes, objects and functions of the standard C++ library. #include int main () { std::cout << "Hello world!\n"; return 0; }

Preprocessor Directives #include “I want to use a predefined library called iostream” Always start with a ‘#’ iostream: a library for inputs (from e.g., a user) and outputs (to e.g., the monitor)

“using” Directives using namespace std; “I want to use objects in a name group ‘std’ ” Tells the compiler where to look for names in the library Can deal with the situation where two or more objects in different libraries share a same name (naming confliction). –Read Appendix N for more about namespace

main function int main() The main body of the program. Compiler first tries to locate “main()” to find where to begin the program In the form of a function –I will cover “function” soon

Comment Internal program document Not considered as a program code Start of comment End of comment Start of comment End of comment

Nested Block Comments are Invalid

Variables Named memory locations that have a type –Named: identifier –Type: needs declaration What you can do with variables –Storing data –Modifying data –Reading data

Variables and Identifiers Memory Address of memory: Hard to remember Identifier: name of address

Variables and Identifiers Memory studentID studentGrade1 studentGrade2 Identifiers

Variables and Identifiers Memory studentID studentGrade studentName Compiler keeps track of [identifier-address] table

Variables and Identifiers In program studentID_Total_Grade = studentGrade1 + studentGrade2

Naming Identifiers Allowed characters: A-Z, a-z, 0-9, _ (underscore) Not allowed to start with a digit. E.g., 3class (x), class3(o) The identifier cannot duplicate a reserved word. e.g., if, case, while… Good names  descriptive but short C++ is case sensitive; PI, Pi and pi are different.

Standard Data Types

Integer and Floating Point Types 2 or 4 Bytes 4 Bytes 2 Bytes 8 Bytes 10 Bytes 4 Bytes Size of value type depends on computer architecture

Maximum/Minimum of Integer Value Type TypeSignByteMinimum valueMaximum value short int/short signed 2 -32,76832,767 unsigned065,535 int (PC) signed 2 -32,76832,767 unsigned065,535 int (Mainframe) signed 4 -2,147,483,6482,147,483,647 unsigned04,294,967,295 long int/long signed 4 -2,147,483,6482,147,483,647 unsigned04,294,967,295

Maximum/Minimum of C++ data types

Variables Declaration

Variable Initialization Variable declaration ≠ variable initialization Should be initialized by a programmer before it is used e.g., int count;  declaration (o), initialization(x) char grade = ‘d’;  declaration (o), initialization(o)

Constants Data values that cannot be changed during program execution E.g., – –‘d’ –“Hello word” –‘\0’

To Remember A character constant is enclosed by the single quotes. (e.g. ‘a’) Use double quotes for string constants. (e.g. “Jeon, Seokhee”) bool types are treated as a number. True: non-zero. False: zero.

Standard streams A mapping between data and input/output device

More about cout width(int) function sets the width for printing a value Only works until the next insertion command comes int x = 42; cout.width(5); cout << x << ‘\n’; // Outputs 42

More about cout fill(char) function sets the fill character. The character remains as the fill character until set again. int x = 42; cout.width(5); cout.fill(‘*’); cout << x << ‘\n’; // Outputs ***42

More about cout precision (int) sets the number of significant digits of float type numbers float y = ; cout.precision(1); cout << y << '\n'; // Outputs 2e+01 cout.precision(2); cout << y << '\n'; // Outputs 23 cout.precision(3); cout << y << '\n'; // Outputs 23.1

More about cout Output Manipulators (not a function) endl - outputs a new line character, flushes output dec - sets int output to decimal hex - sets int output to hexadecimal oct - sets int output to octal #include int x = 42; cout << oct << x << endl; // Outputs 52\n cout << hex << x << endl; // Outputs 2a\n cout << dec << x << endl; // Outputs 42\n

Example codes reading (Program 2-2) #include using namespace std; int main (void) { int a; int b; int c; int sum; cout << "Welcome. This program adds\n"; cout << "three numbers. Enter three numbers\n"; cout \n"; cin >> a >> b >> c; // Numbers are now stored in a, b, and c. Add them. sum = a + b + c; cout << "\nThe total is: " << sum << "\n"; cout << "\nThank you. Have a good day.\n"; return 0; }// main Welcome. This program adds three numbers. Enter three numbers in the form: nnn nnn nnn The total is: 66 Thank you. Have a good day. Welcome. This program adds three numbers. Enter three numbers in the form: nnn nnn nnn The total is: 66 Thank you. Have a good day.

Try to understand other examples in textbook! Program 2-3 ~ 2-13