If Statements

if (expression
   Statement 1
Statement 3

if (expression) 
   Statement 1
else
   Statement 2
Statement 3

If you want more complex blocks (more than a single statement) you need to use {}
```
    if (condition) {
       statements A
    } else {
       statements B
    }
```
Note the indentation here, we really use this to identify blocks
- From now on, basic blocks will be indented 3-8 spaces, your choice
- I try to use 4.
In general, I always use {} in blocks, so when you add lines later.
Write a program that calculates the real roots of a quadratic equation.

Nested IF statements

You can nest if statements anyway you want
- Use {} to mark the blocks
- Make sure that you indent.

It is useful to add the missing else if statement

   if (score > 89.5) {
      grade = 'A'; 
   }
   if ((score > 79.5) && (score < 89.5) )  {
      grade = 'B';
   }
   ...

   BECOMES

   if (score > 89.5) {
      grade = 'A'; 
   } else if (score > 79.5) {
      grade = 'B';
   }
   ...

Write a program that reads in a score and prints out the letter grade.

File Streams

Can be tested to see if they are at the end of the file.
Or have had invalid imput attempted
Or are associated with a nonexistant file.
if (filestream)
- true (or then clause) if stream is ok
- false (or else clause) otherwise

Pre/Post conditions, debugging

A precondition is something that is true before a module begins executing
A postcondition is something that is true after a module has finished executing
Often these are recorded in the comments of a program.
When debugging, make sure that you test all paths through your program
This will require a plan, to make sure you have hit everything.

Write a program that reads in a price, and an exchange code, and computes the price in the new exchange (dollars to pounds, lyra, ...)