1. CSC 107 – Programming For Science

2. Announcements

3. The Week’s Goal

4. Variable Declarations  Variables must be declared before can be used  Way of getting computer to make space for variable  States how to interpret memory in future uses  Allows the compiler to check if uses are legal

5. Variables, Constants, & More General CasesExamples Variable Declaration dataType name; dataType name = value; dataType name, anotherName; dataType name = value, anotherName; int count; bool monkey = true; char help,letter; char a=‘a’,letter; Constant Declaration const dataType name = value; const double PI=3.1; Symbolic Constant #define NAME value #define AGE 34

6. Data Types  Each variable also has data type  How program treats variable’s value defined by this  Single true or false value held by bool  C/C++ defines 7 numeric data types  Integer types: short, int, long, long long  Decimal types: float, double, long double  char data type used to store a character

7. Variable Names  Begin with letter or underscore ( _ )  Then use any letters, numbers, or underscore  Unique name * needed for each variable  Computer wouldn't know which of 1,000 bob s to use  Reserved words are… reserved and can't be used  Includes all type names on p. 83 of book  void, unsigned, class also reserved words

8. Program Outline  Once upon a time…  … some stuff happens…  … and they all lived happily ever after

9. Program Outline  Once upon a time…  All programs must begin somewhere  Defines what is worked upon during rest of program  For non-trivial programs, requires receiving input  When starting program, first steps always same: 1. What is the input? 2. What will the input look like? 3. How will the data be entered?

10. Reading From The Keyboard  Easiest to get input from the keyboard  Reading from files possible; discussed later in term  C++ lacks standard, so writing GUI much harder  C++ defines cin to get user’s input  As easy to use as delivering food to Granny’s house  When cin hit, program waits until it has input  User must press enter for line to be able to be read  Editing not seen by program; only receives final line

11. Programming Using cin  Used to read one or more values at once: cin >> variable ; cin >> variable1 >> variable2 ;  Reads where last cin stopped reading input  Automatically skips past whitespace  Data type of variable determines what is read  Stops reading at first non-usable value in input  If input is not usable, will set variable equal to 0

12. cin Example >>

13. cin Example >>

14. cin Example >>

15. Program Outline  Once upon a time…  Get the input using cin from the keyboard  Can use cin any time, but usually precedes cool stuff

16. Program Outline  Once upon a time…  … some stuff happens…  Want to do something with variable declared  C++ has large variety of statements to do this  First statement covered in today’s lecture

17. Program Outline

18. Assignments  Variable declaration creates “box” to store data  Box can get values placed in it using assignments  General form of assignment is variable = expression;  Computer works by first evaluating expression  Single value must result from this expression  Value of variable set to this result

19. What Is The Expression ?  Simplest expressions are literal values  Examples: double d; int i; char doe; i = 6; i = 7; d = -7; d = 34.5691; doe = ‘a’; doe = ‘0’; 125612.345-56‘a’

20. What Is The Expression ?  Examples of other simple expressions double d; int i; char doe; i = 6; i = 7; d = -i; i = d; d = 34.5691; i = d; doe = ‘0’; // 0 == ASCII 48 i = doe; doe = i;

21. Data Types  Assignments are legal only if always safe  C++ defines ordering of legal assignments long double double float long int short char Legal to assign to higher type

22. What Is The Expression ?  Can also include basic arithmetic operators  Addition +i = 4 + 6;  Subtraction -d = i – 2.3;  Multiplication *i = 120 * 8;  Division /d = 4.0 / i;  Modulus %i = 120 % 8;  Modulus computes remainder between two integers: 4 % 5 equals 4 5 % 4 equals 1 9 % 3 equals 0 12823 % 812 equals 643

23. Tracing A Program  Important for understanding & debugging code  Step-by-step execution of program shown  To see what is happening, done via pencil-and-paper  Execute each line of program like computer does  Within trace, add row whenever variable declared  Update variable’s value each time it is assigned  Off to side, show any output from cout statements

24. Program Trace 1 int x = 4 + 2; 2 int y = 8 * 1; 3 double z = y – 3; 4 x = x + 1; 5 y = 7 % x; 6 z = y + 1.0 / 2.0; 7 z = 8.0 / 4 + x * x; 8 y = (x – 3) * (y + 2); 9 y = x / 4; 10 cout << x << “ ” << y << “ ” << z << endl;

25. Integer Division  Dividing two integers computes an integer  Literals or variables does not matter, only their type.0  Important to remember, 12 is integer & 12.0 is not  C++ ignores result after decimal to get integer 2 / 5 equals 0 (the.4 was thrown away) 5 / 2 equals 2 (the.5 was thrown away) 16 / 4 equals 4 -5 / 2 equals -2 (the.5 was thrown away) 2.0 / 5 equals 0.4 ( 2.0 is not an integer!)

26. Floating Point Arithmetic  Operations using decimal has decimal result  Even if whole number is result of the operation  For example, all the assignments to i are illegal: int i; double d = i; i = 6.0 / 3.0; i = 2.0 * d; i = d + 1; i = 4 * 2.0; i = (d * 1) + 5; i = 8 + (9 * 3) – (2 / 1.0) * 4 + 2;

27. Priority of Operations  Equations can become very complex  4 + 5 * 6 * 9 - 2 + 1 = …?  Very  Very strict order of operations used by computer  ( ) Solve from inner- to outermost  + (positive) & - (negative) Solve from right to left  * & % & / (division) Solve from left to right  + (addition) & - (subtraction) Solve from left to right use lots of parentheses  My suggestion: use lots of parentheses

28. Compound Assignment Operators  Short simple operators that allow us to be lazy  Save some typing for several common actions  Lowest priority operation; expression evaluated first OperatorEquivalent C++ Expression a += 2;a = a + 2;a = a + 2; b -= d;b = b – d;b = b – d; c *= 4 + 5.6;c = c * (4 + 5.6); d /= 0.3 * e;d = d / (0.3 * e);

29. How To Shoot Yourself in Foot  Also increment ( ++ ) & decrement ( -- ) operators  Use with variables only; no exceptions possible  Used anywhere to save typing an additional line  Two different ways these operators applied v = ++b % c;  b = b + 1; v = b % c; c = f * --h;  h = h – 1; C = f * h; a = b++ * c;  a = b * c; b = b + 1;

30. Program Outline  … and they all lived happily ever after  All good processing comes to end & report results  Shows program worked and provides feedback  Results takes many forms, focus on printing today  When starting program, last part asks: 1. What must be output? 2. How can output be presented best? 3. Will it be pretty?

31. Using cout to Print  Already seen how to print text using cout cout << “Hello World” << endl;  Prints out whatever is placed between quotes  endl goes to next line and prints out immediately  Use escape sequences for fancier text output \n  newline (move to start of next line) \t  tab (go to next column that is multiple of 8) \\  \ (backslash character) \”  “ (quotation mark)

32. Can Print Out Multiple Items  cout can also print out value of variables int bob = 2; double j = 4.5; char var = ‘a’; cout << “Hello ”; cout << bob << endl; cout << j << endl; cout << var << endl; cout << j << “ is not ” << bob << endl; cout << bob << “ equals bob” << endl; cout << var << bob << j << endl;

33. But Can It Be Used?  cout built to provide basics needed to work  Prints out as many digits as needed  No extra spaces or tabs used  Scientific notation cannot be used  Often want to format results  Significant digits can matter  Tables make reading faster

34. Real World Strikes Again TrollPrincess

35. First Way To Format Output #include using namespace std; int main() { int k = 4; cout << k << endl; cout.width(4); cout << k << endl; cout << k << endl; cout.setf(ios::showpos); cout << k << endl; cout.width(3); cout.setf(ios::left); cout << k << k << endl; }

36. Second Way To Format Output #include #include using namespace std; int main() { int k = 4; cout << k << endl; cout << setw(4) << k << endl; cout << k << endl; cout.setf(ios::showpos); cout << k << endl; cout.setf(ios::left); cout << setw(3) << k << k << endl; }

37. Your Turn  Get in groups of 3 & work on following activity

38. For Next Lecture  Read sections 6.7 for Thursday  What do we mean by order of operations?  Week #1 weekly assignment due today  Problems available on Angel  If problem takes more than 10 minutes, TALK TO ME!  Week #2 weekly assignment posted today  Will be due week from today