C++ Program: Counting Fingers

1. Chapter 2 Overview of C++

2. A Sample Program // This is my first program. It calculates and outputs // how many fingers I have. #include <iostream> using namespace std; int main () { int digits; digits = 5*2; cout << "I have " << digits << " fingers" << endl; return 0; }

3. C++ Language Elements • Comments • Compiler directives • Function main • Declaration statements • Executable statements

4. Comments • Used to explain code to author and other readers • /* */ (multi-line, "C style") • // (until end of line, "C++ style") • Write good meaningful comments! • There is a bad example on class page under: Other Useful Links • Don't repeat code in a comment, explain it!

5. #include <filename> • this is a compiler directive (starts with #) • 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

6. using namespace std; • Indicates to compiler that this program uses objects defined by a standard namespace called std • The statement ends with a semicolon • Follows #include directives in the code • Must appear in all programs

7. The main function • Every C/C++ program must have a function named main and only ONE called main • The start of the main function is the marker for the start of the program execution int main ( ) { // function body return 0; }

8. type of returned value () says no parameters name of function What is in a function heading (header)? int main( ) 8

9. The main function • header is int main () // NOT "void main" • empty () in header means no parameters, indicates no special information passed to the function by the operating system • braces {} around body must balance • semicolons mark ends of statements • return 0; at the end of the function "satisfies" the int return value in the header

10. Code and Data • Almost every statement in the program is concerned with manipulating data • inputting it • outputting it • calculating with it • making decisions based on its values • storing it temporarily or permanently

11. Data Properties • has a name - either itself or an identifier • has a type - integer, character, float, string, etc. • has space in RAM and an address = memory allocated to hold its value • has a value - 7.2, -3, 'd', true, "John" • can be referred to as a variable (avg or sum) OR a namedconstant (PI or MAX) OR a literal constant (4 or "abc")

12. Reserved Words (Keywords) • Have special meaning in C++ • Cannot be used for other purposes • Ones we have seen • main • include • using • return • int

13. Identifiers - the names of data and functions • syntax rules for making 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 • case sensitive!! Upper vs. lower case • cannot be a reserved word • they are used for names of variables, named constants, or functions

14. Identifiers • VALID age_of_dog taxRateY2K PrintHeading ageOfHorse • NOT VALID (Why?) age# 2000TaxRate Age-Of-Catint

15. Data types • The type determines which values can be used and the operations you can perform • Types protect you from making logical mistakes - mixing types in ways that don't make sense - adding a string to a float • "strongly typed" languages versus "weakly typed" languages • C++ versus Visual Basic

16. Data Types • int, float, double - all numeric • fractional part (float) versus no fractional part (int) • exponential notation for floats / doubles • overflow, underflow • char - holds ONE character • string - zero or more characters in an object • bool - logical values (George Boole) - true, false

17. Data Types (con’t) • Floating point (real) • number has two parts, integral and fractional • e.g. 2.5, 3.66666666, -.000034, 5.0, 5.4E10 • float, double, long double • stored internally in binary as mantissa and exponent • Exponential or scientific notation for very large and small numbers (upper or lower case e) • 10.0 and 10 are stored differently in memory

18. Data Types (con’t) • Boolean • named for George Boole • represent conditional values • values: true and false • used for storing results of comparisons for later use "flags" • not used for input or output

19. 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’ ’\a’ ’\r’ ’\t’ ‘\\’

20. string Class • Strings not built-in, but come from library • A string literal is enclosed in double quotes E.g.: “Enter speed: “ “ABC” “B” “true” “1234” • #include <string> • for using string variables, but not needed for literals

21. Declarations of data • All variable and function identifiers must be declared before use and can only be declared ONE time (in one scope) • Constants • literal constants ('a', 4, 5.2, true, false, "John") • Don't need declarations, their names are their values • named constants (PI, MAX) usually all caps • Must be declared and given a value at one time

22. What Does a Variable Declaration Do? int ageOfDog; float taxRate; char middleInitial; A declaration tells the compiler to allocate enough memoryto hold a value of this data type and to associate the identifierwith this location - its value can be changed many times during the program run 4 bytes for taxRate 1 byte for middleInitial

23. What does a variable declaration NOT do? • Note that the previous slide did not mention the _starting or initial value_ of the variables • A plain declaration of a variable does not give the variable a starting value - do NOT assume it is zero or blank or any known value • You do not know the value of a variable until YOU give it one • to declare and initialize at one time • "int x = 5;" "declaration with initialization"

24. What is a Named Constant? A named constantis a location in memorythat can be referred to by an identifier and in which a data value that cannot be changed is stored Valid constant declarations const string STARS = “****”; const float NORMAL_TEMP = 98.6; const char BLANK = ‘ ’; const int VOTING_AGE = 18; const float MAX_HOURS = 40.0; Why use them? good documentation, easy to edit later, prevents typing errors Identifiers usually upper case, by custom

25. Program Style • Use of spacing and blank lines • one statement per line • blanks after comma, around operators • in between some lines of code for readability • Use of comments • header comments at the top of the file - name, date, email, section, PURPOSE • document algorithm steps • describe difficult code

26. Block(Compound Statement) • A block is a sequence of zero or more statements enclosed by a pair of curly braces { } SYNTAX { Statement, statement, . . . } • Braces should line up and statements inside should be indented • Blocks are used for the body of a function, as well as grouping statements together

27. Executable statements (to start with) • Output statements • Input statements • Assignment statements • Return statement

28. Input Statements • Obtain data for program to use - different each time the program executes • cin - name of standard input stream associated with standard input device (keyboard) • Extraction operator (>>) • E.g.: cin >> miles; cin >> age >> firstInitial;

29. Output statements • cout "console output" • cout is the name of the standard output stream • output sent to cout always goes to the screen (standard output device) • insertion operator << • several can be chained in one statement • outputting literals • outputting variables and named constants • endl - a manipulator (ends with "l" - lower case ell, not the digit 1)

30. Output Statements SYNTAX These examples yield the same output: cout << “The answer is “; cout << 3 * 4; cout << “The answer is “ << 3 * 4; cout << Expression << Expression . . .;

31. Return statement • "return 0;" always at the end of the sequence of statements in the main function • semantics: execution control turned back over to Operating System (Windows or Unix) • means the program is over! • return value 0 means "normal exit"

32. Assignment statement • Syntax "var = expression;" • Semantics - left side location gets the value of the expression on the right hand side • Expressions can use operators of appropriate types (arithmetic or string) • The expression must evaluate to ONE value • This one value has a type • either matches type of left hand side or doesn't • type coercion or type casting happens if doesn't

33. Examples: • int x, y, z; x = 5; // expression 5 y = x * 2; // expression x * 2 or 10 z = x + y - 18; // expression x + y - 18 or -3 x = x + 2; // expression x + 2 or 7

34. Working with the IDE • Build versus Rebuild versus Clean • “build is up-to-date” warning - Watch out!! • Errors and warnings • Warning level W2 is what will be used to grade your programs - instructions on how to set this are on the program assignment page

35. Syntax Errors • The compiler may report lots of syntax errors • NO executable generated if there are any! • Fix the FIRST one then recompile • Try to understand what the error was • Error messages are not clear • keep a log of messages and what they mean • Do not ignore warning messages!

36. Logic (Semantic) Errors • Caused by a faulty algorithm • They are only found by testing - compiler does not detect them! • Testing • choose an input value • calculate by hand the expected output • run the program and check the actual output • Test several different input values

37. Runtime Errors • Caused by something the program cannot control in its environment • example: division by zero • example: file not found • usually crashes the program • more advanced - read about 'exceptions'