-----BASIC C++ PROGRAM TEMPLATE-----

#include <iostream> 
using namespace std; 
 
int 
main (int argc, char **argv)
{ 
  /* Variable Declaration */ 
 
 
  /* Instructions */ 
 
  return 0; 
} 
------ COMMENTS ---------------

/* 
   Put explanatory messages for yourself and other
   programmers (not the computer) in comments
   like this one 
*/

//single line comments look like this

------EDIT SAVE COMPILE RUN -------------


or EDIT, SAVE, COMPILE, FIX COMPILER ERRORS, RUN, CHECK OUTPUT

1) Edit your code with an editor like emacs or nano (learning to navigate in at least
one editor on polaris is going to be important for this class)

E.g.   emacs -nw my program.cpp
       OR
       nano myprogram.cpp


Remember to save you changes!


2) Compile your code with a compiler (translates
human readable source code into executable format
the computer needs to actually run the program)
E.g. g++ myprogram.cpp

Fix any compiler errors! 
Go to first problem by it's line number and fix.

3) Run your program 

E.g. ./a.out

Check that the output of the program is what you expect


-----SIMPLE TYPES-----

TYPE	    EXAMPLES
int	    0,1, -1, 2, -2,...
	
unsigned int  0, 1, 2,3, 4, ...

float	    2.89, 67777799.0, -1000000000.0
double

char	    'a', 'Z', '\n'

bool	    true, false


string	    "August", "This sentence is a string"


possible numeric values are not infinite like in math
- e.g. there is a fixed amount of space to store an int
and so unlike in real like there is a maximum integer

unsigned int vs int - use space to store all positives
    vs half positive and half negative

unsigned and int vs float
     float can store bigger and smaller numbers
     but to do so can give up precision

float vs double - more space used for both bigger numbers
and more precise numbers


-----SAMPLE VARIABLE DECLARATIONS------

int month;
char answer;
bool isReady = false;
char initial = 'A';
float wage = 8.50;
string name = "John Smith";
unsigned int year = 1996;

Remember to use descriptive variable names!!


-----INPUT/OUTPUT----

Read data from user into a variable
cin >> variable;

Write data out to user
cout << "Hi\n";
cout << "Hi " << name << "\n";
cout << "Hi " << name << endl;


----- ARITHMETIC OPERATORS-------

+    add
*    multiple
-    subtract
/    divide (remember for ints gives just whole 
	    number part of answer, cuts off any decimal portion)
%    modulus (gives integer remainder after division)

remember order of operations like in math
can use parentheses to force/clarify the order you want

----- ASSIGNMENT STATEMENTS-------

Example assignment statements

hoursPerMonth = daysPerMonth*24;

age = age+1;

index = index -1;

total_price = num_item1 * item1_price + num_item2 *item2_price;
-------------------------------

Normal arithmetic expression:
x = x+1;

A few shortcuts worth knowing that do the same thing:
x++;
++x;

x++  uses x and then increments it
++x increments x and then uses it.

If only use is incrementing then they do the same thing.

------- BOOLEAN EXPRESSIONS --------

boolean expressions evaluate to true or false

Example boolean expressions

bool isTransferStudent;
(isTransferStudent)

(month > 2)

(answer == 'Y')

------ COMPARE OPERATORS  -----------

==  equal
    (Remember one = sets something equal. Two == tests if 
     two things are equal)
    (Also remember that it is dangerous to test doubles with ==
    they may be very very close but not identical in precision)
!=  not equal
>   greater than
>=  greater than or equal
<   less than
<=  less than or equal


------ BOOLEAN OPERATORS ----------

&&     AND
||     OR

Combine boolean expressions to make a larger boolean expression

((month >=1) && (month <= 12))
((answer == 'Y') || (answer == 'y'))


TODO: Practice reading compound boolean expressions to see
if they are true or false 
e.g. What is wrong with one?
((answer == 'Y') && (answer == 'y'))

------ IF STATEMENTS ---------------

if (boolean expression)
{
	true_statement1;
	true_statement2;
	
} 
come_back_to_whether_true_or_false;

if (boolean expression)
{
	true_statement1;
	true_statement2;
	
} else {
       false_statement1;
       false_statment2;
}
come_back_to_here_true_or_false;

Note: Always using {} in your if statments is safer

else clause is optional

Always come back to main line code after the if!!



------ IF-ELSE IF-ELSE STATEMENTS ---------------

if (booleanExpression_option1)
{
	option1_true_statement1;
	option1_true_statement2;
	
} else if (booleanExpression_option2) {
       option1_false_option2_true_statement1;
       option1_false_option2_true_statement2;

} else if (booleanExpression_option 3) {
       option1_false_option2_false_option3_true_statement1;
       option1_false_option2_false_option3_true_statement2;

} else {
       option1_false_option2_false_option3_false_statement1;
       option1_false_option2_false_option3_false_statement2;

}
come_back_to_here_regardless_of_which_option;

Note: 
Take first option that matches even if later ones could have matches also

Evaluated one at a time and take first option
that matches!  Don't take multiple branches
even if match multiple
 
Always have exactly 1 if, can have 0-N else if,
can have 0 or 1 elses

EXAMPLE:

unsigned y;

if (y==1)
{
	cout << "1";	
} else if (y< 10)
{
	cout << "0 or 2-9";

} else if (y==5)
{
	cout << "This will never happen.. do you see why?\n";

} else if (y < 20){

       cout << "10-19";
} else {

       cout << "20+";
}

Boolean expressions can be about different variables

if (sky == BLUE) {
  //if sky is blue it will go here ( even if it is also Friday)
} else if (day == FRIDAY) {

  //fridays but not fridays with blue skies
} else {
  
  //Sat - Thurs where sky not blue
}
----------- NESTED IF STATEMENTS --------------

if (fromTheUnitedStates){

   //what state
   if (fromNY){

   } else if (fromVT){

   .....
   
   } else if (fromOH){

   }    

   fromUS_but_regardless_of_which_state;

} else{
  
   //not from the United States
   //what country
   if (fromCanada){

   } else if (fromMexico){

   .... 
   
   } else if (fromGermany){
 
   }   

   notfromUS_and_regardless_of_which_other_country;
}
regardless_of_whether_US_or_not;


TODO: Practice following the flow of code through
if clauses and nested if clauses.
Debugger is helpful for that.

----------------------------------------------
READING IN MULTIWORD STRINGS

cout << "What is your motto? ";
//XXXX cin will just get the first word
//cin >> motto;
std::getline(cin, motto, '\n');


REMEMBER IMPORTANT DIFFERENCE BETWEEN cin and getline
cin leaves trailing white space like '\n' unconsumed
getline as shown above will consume the '\n'

SO whenever getline follows a cin, must do something like this:

string endOfLastLine;
std::getline(cin, endOfLastLine, '\n');
std::getline(cin, motto, '\n');

------------- Style ---------------------------

Not just a matter of correctness, make code clear,
readable, elegant

How?

- Identation
- Comments
- Good Variable Names
- Consistency
- Go for obviously correct and readable rather than "tricky"

Other ways to add clarity - enums and const variables to
introduce "readable" names rather than numbers


---------------- Enums --------------------------
enum TemperatureScale {CELSIUS=1, FAHRENHEIT, KELVIN, REAUMUR, RANKINE};

enum Month {JANUARY=1, FEBRUARY, MARCH, APRIL, MAY, JUNE, JULY,
	    AUGUST, SEPTEMBER, OCTOBER, NOVEMBER, DECEMBER}; 

Give value to start with ( in both these cases 1), all others
will be given numbers in order starting with that number

------------- Constant Variables -------------------
const double DELTA= 0.00001;

Constant variables cannot be changed later 

const double DELTA= 0.00001;
delta = 0.01;  //COMPILER ERROR!!!!!

------------------------------------------------

Software Lifecycle

1. Analysis and specification of the task (problem definition) 
   Keep in mind that in the real world specification of the problem 
   can change often 
2. Design of the software ( data representation and algorithm design) 
3. Implementation ( coding) 
   Just because have a plan all written out doesnt mean add all the code
   at once - add by spoonfuls and keep compiling
4. Testing 
   Can't do exhaustive testing - chosing which cases to test is a key skill!
5. Maintenance and evolution 
   Keep in mind that good programs are easy to read and modify by others 
-----------------------------------------------------

Designing a loop
   What goes in the body of the loop?  Body Statement
   What is the conditions for ending the loop? Loop Condition
   What will happen in the loop to let the loop end? Update actions 
   What do we need to do to set up for the loop? Initializing statements
   What do we need to do after the loop? Completion actions

----------WHILE LOOP--------------------------


InitializationActions
while ( LoopCondition)
{
	BodyStatements
	UpdateActions
}
CompletionActions     

Example:

int i;
cin > i;
while ( i > 0){
      cout << i << "\n";
      i--; 
}

----------DO WHILE LOOP--------------------------

InitializationActions
do
{
	BodyStatements
	UpdateActions
} while ( LoopCondition);
CompletionActions     

Example:

char answer;
do
{
	cout << "You are amazing!\n";
	cout << "Should I say that again? [y/n]\n";
	cin >> answer;
} while ( answer == 'y');

----------FOR LOOP--------------------------

for (InitializationAction; LoopCondition; UpdateAction)
{
	BodyStatements
}
CompletionActions



More InitializationActions
for (InitializationAction; LoopCondition; UpdateAction)
{
	BodyStatements
	More Update Actions
}
CompletionActions

Example:

int bottle;
for (bottle=99; bottle >1; bottle--)
{
	cout << bottle << " bottles on the wall\n";
}
cout << "1 bottle on the wall\n";
cout << "No bottles on the wall\n";
=======================================

Any loop you want to write can be written using
any of these three styles ( while, do-while or for)

So which  one do you use? Matter of style but generally

      processing an array => for loop
      
      fixed number of iterations => for loop

      
      unsure how many times through loop => while or do-while	

      do-while if do you want the loop body to run at least
          once no matter what


Some easy types of loops to practice


- Count up or down
- Do until the user says to stop
- Loop asking for input until you get valid input
- Loop over an array or multidimensional array doing something to each element
(e.g. stats like total, average, max, min)

Harder types of loops
- Nibble away at a problem a little at a time (e.g. make change, arabic to roman numberals)


=============ARRAYS===================================


Arrays group together many of the same type of object

  float homeworkGrade[10];
  int bigArray[1000];

  int foo[4];
//notice that the first array element is [0] not [1]!!


  foo[0] = 8;
  foo[1] = -9;
  foo[2] = 7853;
  foo[3] = 0;

  for (int i=0; i< 4; i++){
    cout << "foo[" << i << "] is " << foo[i] << "\n";
  }
============= MULTIDIMENSIONAL ARRAYS===================================



int foo[4][2];

Gives you 4*2 = 8 ints 
foo[0][0]
foo[0][1]
foo[1][0]
foo[1][1]
foo[2][0]
foo[2][1]
foo[3][0]
foo[3][1]

just like for loops perfect for traversing arrays
nested for loops perfect for traversing multidimensional arrays

int foo[NUM_ROWS][NUM_COLS];

for (int row=0; row< NUM_ROWS; row++){
    for (int col=0; col< NUM_COLS; col++){
     cout << foo[row][col] << "\n";
    }
}

Can have more than 2D - for example 4D arrray - 

int bar[8][5][3][16];
Gives you 8*5*3*16 = 1920 ints!



================== COMMAND LINE ================

In our basic template we have:
main (int argc, char **argv)

argc is the number if arguments on the command line
and
argv is an array of those arguements (C-style strings)

THis loop will print out all the command line arguements
for (int i=0; i< argc; i++){
    cout << "argv[" << i << "] is " << argv[i] << "\n";
  }

You can use this to pass in values from the user to the program
like the name of a file to open etc. instead of asking the user
a question during the program

===============NESTING========================


All of these constructs ( if, if-else, if-elseif-if,
do-while, while, for) can be combined via nesting

For example an if inside a for inside another if

  if (totalHours >= 40.0){ 
    overtimeHours = totalHours - 40.0; 
 
  } else { 
 
    overtimeHours = 0;
 
    for (int day=0; day<DAYS_PER_WEEK;  day++){
      if (hoursPerDay[day] > 10.0){ 
        overtimeHours = overtimeHours + hoursPerDay[day] - 10.0;
      }
 
    }
  } 
 
Always indent when you start a new level of nesting!
It will help make it clear what is inside or dependent on what