1. Libraries Programs that other people write that help you. #include // enables C++ #include // enables human-readable text #include // enables math functions using namespace std; // enables cout >

2. Keywords vs. myWords Keywords are C++ defined: – int – main – char – double – while – cin – cout – many more variables, file names are your choice Convention: – lowerUpper

3. cout - decimal precision cout only displays 6 decimal characters cout attempts to reduce output to save characters use "cout. precision( n ); " to set displayable values to n decimal characters

4. Scientific notation Try this: double x; x = 35.62 e 6; cout.scientific; cout << x << endl; cout.fixed; //eliminates scientific notation cout.precision(12); cout << x << endl;

5. The Assignment Statement “=” int main ( ) { int A; A = 4; A = A + 3; } NOT “A equals 4” instead: “A is assigned the value 4” semicolon, brackets, main… must be C++

6. Operators The usual: + - / * Precedence: use ( ) e.g. (y + b) * c not the same as y + b * c Negative numbers: - 8

7. Announcements Please read all of Chapter 1 in the text comments operators variable types libraries if statement and comparisons

8. Variables Variables are used to set and change values, which represent quantities, text, or states.

9. How do we use numbers? Counting Measuring Non-numerical designations: Finally, they can designate a “state” unrelated to the number (“1 if by land, 2 if by sea”)

10. So computers Must deal with each type of number in it’s own way Must store those numbers in their own way Must make those numbers available, though, through a common interface That interface, is the “VARIABLE”

11. How computers use info Numbers! Everything is a number! The letter “A” is stored as the number 65 The letter “B” is stored as the number 66 The color RED is stored in three numbers as 255 0 0

15. Variables x, y, z i, j, k totalCountOfNewEmployees any_sensible_name // usually for what // the variable holds They Stand for Something, can be named anything except reserved C++ words

16. Variable Types (primitive, common) Integers – meant to be a whole number (used for counting) C++: int Floating Pt. – meant to be a detailed number (used for measuring) – called a double Character – has no meaning other than to be read by a human – C++: char Strings of Characters – have no meaning other than to be read by a human: string – Not native to C++, but libraries exist to help… Boolean – reflects a state of true or false – C++: bool

17. "x is 14" Could mean 14 Could mean 13.999995 Could mean 14.000001 Could mean 20 (honestly), might not be base- 10, more later Could mean “Fourteen”, which has no meaning other than to be read by humans

18. “Typing” a variable – clarifies what it does and its precision int x; x = 14; Therefore, 14 means 14 double x; x = 14.0000; Therefore, x has meaning, 14 to 4 places

19. note Should be initialized at the declaration int x = 14; // type name = initValue; "typed" = declared Can only be “typed” once Value can be reset (that’s why it’s called a “variable”).

20. floating point (i.e. double)? 14.6567 128.1231 154367.001423 3.14159 987987465986543. “adequate precision” cout rounds numbers for space int x = 45678.34342; cout << x; will DISPLAY as 45678.3, although x will retain its value for calculations

21. once a variable is designed you can get it from the operator (if you want) int x = 1000000; x=0; cout << “enter x: ”; cin >> x;

22. chars and strings #include using namespace std; char Id = 'm'; // chars are single-quoted string name = "mikeb"; // strings are double- quotes int main( ) { cout << Id << endl; cout << name << endl; }

23. New Types  Boolean – true or false (really means presence or absence), used to signify a condition, or “state” of being.  the “bool” type can have values true or false (note: WITHIN the computer, false is zero, and true is any non-zero value).  operations are OR and AND bool X, Y, Z; X = true; (same as = 1, means “X is present”) Y = false; (same as = 0, means “Y is NOT present”) Z = X OR Y; (what is Z?, i.e. does Z signify some presence?) Z = X AND Y; (what is Z?)

24. George Boole said that all life could be explained as a combination of things that were present or absent under certain conditions. Really, just a way of describing things with simple math symbols.

25. A smoke, water, burglar alarm Boolean variables W, B, S, A W is true if water B is true if burglar S is true if smoke A means “sound the alarm” A = W and B and S Does W and B and S make sense? A = W or B or S

26. The "if..else" statement if ( a == b ) { // do this } else if ( a < b ) { // do this } else { // do that } conditionals

27. "logical" comparisons if ( a == b ) if ( a != b ) if ( a < b ) if ( a > b ) if ( a <= b ) if ( a >= b )

28. if demo #include

29. a simple menu #include using namespace std; int main() { bool quit = false; int choice = 0; while ( quit == false ) { cout > choice; if (choice == 0) { quit = true; } else { cout << "loop again..." << endl; } } // end while return 0; } // end main Loop ( iteration ) conditional

30. Legality Variable value and variable type must be the same. Deterministic behavior - All computers yield the same result with the same variables

31. Computers DO NOT completely check our programs Called “Compilation” Must be successful before a program can “run” But not all errors are caught in compilation

32. So, Illegality is... “Compiler” Errors – however, some languages and compilers allow mis-designations of variables Indeterminate results “Run-time” Errors - only show up when you run the program

33. Illegal #1 – mis-defined variables int y; y = 14.0001; char q; q = "abcdef"; double z; z = "hello";

34. Why “Type” Variables Deterministic behavior of variables and the numbers they represent. New definition of “Legality” : We will never perform mathematical or logical operations on variables of different types.

35. Illegal #2 – mixing variables in same equation int x; double y; char z; x = 12; y = 16.001; z = x + y;

36. Illegal #3 - Operation wrong for variable type: char Q, R, S; Q = R / S; // remember "/" is divide