Finishing Intro to Algorithms.

There are two "control structures" we use when programming.
- These change the way the program executes.
- selection or if
- Repetition or looping.
In our first algorithm
- ```
get miles to travel
get price of gas
get miles per gallon

cost = price of gas / miles per gallon  * miles traveled

print cost 
```
- We just did the instructions in order.
- This matches what we know about the PC from the architecture model.
- do the first instruction, then the next, ...
Selection or an IF statement allows us to skip some instructions in the sequence.
- For an if statement, we need to make a decision.
- This decision needs to be written as a yes-no question.
- We will call this a boolean expression.
  - This is why you will study this in discrete math.
- In pseudo code we would write something like
```
if condition then
   instructions if condition is true
else
   instructions if condition is false.
        
```

How about my routine in the morning

wake up
eat breakfast
if it is a school day
   get dressed and go to school
else
   stay home and do something fun

Sometimes we might not have the else part.

Think about leaving the house in the morning

get dressed
if it is cold out
    put on a coat
get in the car
go to school.

Sometimes it is a complex set, so we use elseif

My weekly routine

if it is Monday or it is Wednesday or it is Friday
   Go to Programming II
   Go to Intro to CS
   Go to CSCI Systems Programming 
else if it is Tuesday or it is Thursday
   Go to Object Oriented Programming
else if it is Saturday
   Do Saturday things.
else
   DO Sunday things.

Languages have different ways to implement selection, but the idea remains the same.
Repetition is the second major control structure
We can use various words, but while is very common
- These also take a decision
- And they repeat generally while the condition is true.

My Life

while the semester is in session
   do My Weekly Routine.

Additionally we could use ideas like foreach thing in a collection

Grading

for each homework that was submitted
   grade the homework
   put the grade in the grade book
   provide the student with feedback.

A final step is procedures.

This is natural in real life, but somewhat harder (in the beginning) for programmers.
This is really abstraction.
Does grade the homework really provide sufficient instructions for grading in the above algorithm?

Could we provide more detailed instructions?

for each question 
   look at the answer and judge
      does it answer the question?
      Is it correct?
      Is it well formed?
   Assign points based on the answers to the above answer the question?

Can we write an algoirthm that will convert from base 10 to base 2?