1. CS31: Introduction to Computer Science I Discussion 1A 4/2/2010 Sungwon Yang swyang@cs.ucla.edu

2. Programming Language Here are examples: – In English: Hey Computer, say “Hello!” – In a programming language, C++: cout << “Hello!” << endl; – In a machine language: 010001011010011100100100100101 (or something similar to this)

3. Programing Language Programmers – Translate human language into programing language Writing C++ code Compilers – Translate programing language into machine language Making executable file

4. Example 1 Print out a text on the screen

5. Some Basic Rules #include – Contains libraries related to input & output using namespace; – Just write this statement at this point int main() – Your program start from this function Every statement ends with a semicolon – Missing semicolon will cause compile error Case sensitive – C++ distinguishes between upper and lower case Text needed to be double-quoted – Otherwise, C++ will recognize it as something else White spaces

6. What can we learn from the example cout object – Print out “text” on the screen – Basic syntax cout << “what you like to write”; – endl New line cout << “what you like to write” << endl; – << Careful with the direction Not >> – You can use more “text” cout << “what you like to write” << endl << “more words”;

7. Quick question What will be displayed on the screen? #include using namespace std; int main() { cout << "Hello!" << "My na"; cout << "me is Sung"; cout << endl << "won. What is" << endl; cout << "your " << "name" << endl << "?" << endl; }

8. Answer Hello!My name is Sung won. What is your name ?

9. Quick Question Can you find any mistakes? Hint: 7 mistakes include Using name space std; int main() { cout << "Hello!" << "My na"; cout << 'me is Sung'; cout << endl << "won. What is" << endl cout > "name" << endl << "?" << endl;

10. Answer include Using name space std; int main() { cout << "Hello!" << "My na"; cout << 'me is Sung'; cout << endl << "won. What is" << endl cout > "name" << endl << "?" << endl; Double quote! Should be lower case No space! ; is missing # is missing Wrong direction } is missing

11. Example 2 Input from keyboard #include using namespace std; int main() { int age ; age = 0; cout << "How old are you?" << endl; cin >> age; cout << "I am " << age << " years old." << endl; }

12. What can we learn from the example Variables – “data storage” – int age; Declaration: prepare space for ‘age’ int: integer age: identifier, name of variable – age = 0; Assign 0 to age

13. Data types int : integer – 4 bytes long – ranging from -2,147,483,647 to 2,147,483,647 double : real numbers – 8 bytes long – ranging from −1.7 × 10 308 to 1.7 × 10 308 bool : boolean – 1 byte long – either true or false (IGNORE FOR NOW) char : character, – 1 byte long, holds an ASCII character (IGNORE FOR NOW) string : string – let’s talk about this later

14. Identifiers – An identifier must begin with an alphabetic character (a-z or A-Z) or an underscore(‘_’), which may be followed by alphabetic/numeric (0-9) characters and underscores. – Cannot use keywords (reserved words) using, int, double, etc… Quick questions!

15. What can we learn from the example cin >> age; – Get user’s input from keyboard – Assign the input to age – Be careful with the direction Opposite direction of the case of cout cout << "I am " << age << " years old." << endl; – we can use variable in cout – No quotes!!

16. Quick question age is integer type variable – What if input numbers with a decimal point? The range of int is from -2,147,483,647 to 2,147,483,647 – What if input numbers out of range?

17. Comment Compiler will ignore comments We can insert comments in a C++ program – Use double-slash: // Comment for single line – Use /* and */ pair Comments for multiple consecutive lines